feat: add rust toolchain and shell completions

[manuelmauro]

Summary

• Pin the Rust toolchain via rust-toolchain.toml (1.92.0 with rustfmt and clippy), matching the setup in skilo.
• Add a self command group whose completions subcommand prints a shell completion script to stdout, generated with clap_complete.

Shell completions

arkouda self completions <shell> supports bash, zsh, fish, powershell, and elvish:

# Bash (add to ~/.bashrc)
eval "$(arkouda self completions bash)"

# Zsh (add to ~/.zshrc)
eval "$(arkouda self completions zsh)"

# Fish (add to ~/.config/fish/config.fish)
arkouda self completions fish | source

Changes

• Cargo.toml: add clap_complete dependency.
• src/cli.rs: self group + SelfCommand::Completions, CompletionsArgs, and a Shell value enum.
• src/commands/completions.rs: generate completions to stdout.
• src/main.rs: dispatch the nested self completions subcommand.
• src/telemetry.rs: map the self group in Command::name().
• README.md: document the command and toolchain.

Test plan

• cargo fmt --all -- --check, cargo clippy --all-targets --all-features -- -D warnings, and cargo test --all (28 passing) all clean via the pre-commit hook.
• Verified arkouda self --help lists completions and arkouda self completions zsh emits a valid script.

Summary by CodeRabbit

• New Features

  • Added shell completions support via self completions command for bash, zsh, fish, PowerShell, and Elvish shells.

• Documentation

  • Updated documentation with shell completions installation and usage instructions.

• Chores

  • Pinned Rust toolchain version and enabled development tools configuration.

[coderabbitai]

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ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: ecd872d8-6971-4045-840b-016a2d1afd2a

📥 Commits

Reviewing files that changed from the base of the PR and between cdbabc0 and f1a2fc4.

📒 Files selected for processing (2)

• CHANGELOG.md
• src/cli.rs

📝 Walkthrough

Walkthrough

This PR adds a new self completions subcommand that generates shell completion scripts for bash, zsh, fish, PowerShell, and Elvish. The implementation uses the clap_complete crate and includes CLI contract definitions, command dispatch wiring, telemetry integration, and user-facing documentation.

Changes

Shell Completions Feature

Layer / File(s)	Summary
CLI contract and dependencies src/cli.rs, Cargo.toml	Command::SelfCmd variant holds SelfArgs, which nests SelfCommand::Completions with CompletionsArgs. CompletionsArgs accepts a Shell enum supporting five shell types. The clap_complete crate is added as a dependency.
Completions command implementation src/commands/completions.rs, src/commands/mod.rs	The completions::run() function generates shell-specific completion scripts by mapping the Shell enum to clap_complete shell types, constructing the CLI command, and writing output to stdout.
Main dispatch and telemetry src/main.rs, src/telemetry.rs	src/main.rs imports SelfCommand and routes Command::SelfCmd to the completions handler. src/telemetry.rs registers the "self" command name for telemetry events.
Documentation and toolchain configuration README.md, rust-toolchain.toml	The README documents the self completions command and provides shell-specific setup instructions. The toolchain is pinned to Rust 1.92.0 with rustfmt and clippy enabled.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Poem

🐰 A new command hops forth so bright,
Shell completions done just right!
From bash to fish, each shell's a friend,
Arkouda's helpers now extend!
🌟✨

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 50.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately summarizes the main changes: adding Rust toolchain pinning and shell completions support.
Description check	✅ Passed	The description covers all required template sections: Summary (what and why), Changes (key files modified), and Test plan. All critical information is present.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch feat/shell-completions

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[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@src/cli.rs`:
- Around line 117-129: The ValueEnum-derived Shell enum currently
lowercases/kebab-cases the PowerShell variant, causing the CLI to expect
"power-shell" instead of "powershell"; fix this by adding an explicit value name
on the PowerShell variant (annotate the PowerShell enum variant so ValueEnum
uses "powershell" as its canonical name), keeping the #[derive(ValueEnum)] on
Shell and leaving other variants unchanged so the completion command accepts
"powershell" as documented.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: ffc6685a-b339-4783-acc0-eb7fa0fa5710

📥 Commits

Reviewing files that changed from the base of the PR and between f4ebf35 and cdbabc0.

⛔ Files ignored due to path filters (1)

• Cargo.lock is excluded by !**/*.lock

📒 Files selected for processing (8)

• Cargo.toml
• README.md
• rust-toolchain.toml
• src/cli.rs
• src/commands/completions.rs
• src/commands/mod.rs
• src/main.rs
• src/telemetry.rs