Add address lookup table (v0) composition support

[sebscholl]

Adds address lookup table support to the composer layer (bumps the gem to 0.1.7): compose v0 transactions through existing tables, and create/extend tables on chain — with a single clean compile path rather than legacy/v0 branching.

What's included

• TransactionComposer#add_address_lookup_table(account:, addresses:) registers a table and opts the transaction into the v0 format (tracked as explicit version state, not derived from whether tables are empty). compose_transaction resolves every loadable account (a non-signer that is not the fee payer and not an invoked program id) through the tables in a single pass over the tables; merge folds another composer's tables in, deduped by account.
• AccountContext#compile(loaded_accounts:) rebuilds index_of against the combined v0 account space ([static..., loaded...]) while keeping only the static keys in accounts (what the message serializes) and dropping loaded accounts from the header. With no loaded accounts the legacy compilation is byte-for-byte unchanged.
• Solace::Accounts namespace for on-chain account models, with Accounts::AddressLookupTable — a table's address + stored addresses, .deserialize for reading on-chain state, and #reference for the v0 message reference it contributes.
• AddressLookupTableProgram Create/Extend composers + instruction builders, so tables can be provisioned on chain.
• Connection#get_slot.

Notes for review

• Replaces the branching/mutating approach (an if empty? fork + a post-hoc relocate_loaded_accounts that hand-patched the header) with one compile path and a loaded-aware AccountContext.
• Metrics/ClassLength raised to 125 (our own dial) rather than compacting unrelated methods.
• Out of scope: Freeze/Deactivate/Close composers, and a Connection#get_address_lookup_table fetch helper.

Testing

• Static instruction-builder tests; Accounts::AddressLookupTable unit tests (deserialize/reference/initialize); AccountContext loaded-compile unit tests.
• Behavioral (validator-backed) coverage: create, extend, and use — v0 transfers landing on chain with balances/state asserted across single-table, multiple-table, mixed static+loaded, first-table-wins, and readonly-loaded (SPL token) scenarios.
• rake test: 373 runs, 0 failures · rubocop: clean.

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