Add is_max_settlement FIX

[Mitch5000]

Pull Request Title:
Fix max settlement amount configuration ambiguity

Pull Request Description:

Summary

This PR fixes an audit-trail ambiguity in the max settlement amount configuration.

Previously, max_settlement_amount(env, asset) returned 0 both when:

set_max_settlement_amount(asset, 0) was explicitly called by an admin
set_max_settlement_amount was never called for that asset
Because 0 disables the cap, those two states were indistinguishable on-chain.

This PR adds a configuration-status accessor so clients and auditors can distinguish “never configured” from “explicitly configured to zero”, without changing the actual open_settlement cap enforcement behavior.

Changes Made

Added storage helper
File:
src/storage.rs

Added:

has_max_settlement_amount(env, asset) -> bool

Behavior:

Returns false when MaxSettlementAmount(asset) has never been written.
Returns true after set_max_settlement_amount has been called for the asset.
Returns true even when the configured value is 0.
Extends TTL when the entry exists, matching the existing max settlement amount read behavior.

Added public contract read view
File:
src/lib.rs

Added on-chain contract function:

is_max_settlement_amt_configured(env, asset) -> bool

Note:

The originally requested name, is_max_settlement_amount_configured, exceeds Soroban’s 32-byte contract function name limit.
To satisfy Soroban’s function symbol limit, the exported on-chain function uses amt instead of amount.

Also added a Rust client convenience alias:

is_max_settlement_amount_configured(asset) -> bool

This preserves the issue terminology for Rust tests and client-side usage while keeping the actual exported contract function valid.

Preserved open_settlement behavior
File:
src/lib.rs

The cap enforcement logic remains unchanged:

cap == 0 means disabled
cap > 0 enforces the maximum settlement amount

No settlement enforcement behavior was changed.

Added regression tests
File:
src/test.rs

Added and extended tests covering:

Never-configured max settlement amount returns:
max_settlement_amount(asset) == 0
is_max_settlement_amount_configured(asset) == false

Explicit zero configuration returns:
max_settlement_amount(asset) == 0
is_max_settlement_amount_configured(asset) == true
open_settlement still allows settlement because zero disables the cap

Nonzero configuration returns:
max_settlement_amount(asset) == configured value
is_max_settlement_amount_configured(asset) == true

Safe read behavior for an unconfigured asset.

Updated documentation
File:
README.md

Documented the new max settlement configuration-status view.

Dev dependency update
File:
Cargo.toml
Cargo.lock

Enabled the Soroban SDK testutils feature for dev-dependencies so the existing test suite compiles and runs correctly.

Soroban function-name compatibility fix
File:
src/lib.rs
README.md

While validating the build, Soroban rejected an existing public function name because it exceeded the 32-byte contract function name limit:

list_settlements_by_anchor_and_asset

This was shortened on-chain to:

list_settlements_by_anchor_asset

A Rust client compatibility alias was added so existing Rust tests and client code can still call:

list_settlements_by_anchor_and_asset

Validation

Ran formatting check:

cargo fmt --all -- --check

Result:

Passed

Ran full test suite:

CARGO_BUILD_JOBS=1 cargo test

Result:

239 passed
0 failed

Ran build:

cargo build

Result:

Passed

Notes

The build still emits existing Soroban deprecation warnings related to env.events().publish usage. These warnings are unrelated to this fix and were not introduced by this PR.

Files Modified

Cargo.toml
Cargo.lock
README.md
src/storage.rs
src/lib.rs
src/test.rs

Files Created

None

Confidence

96%

The fix directly addresses the described ambiguity, preserves settlement cap behavior, adds regression coverage for all required states, and passes the full test suite and build.

Closes #109