feat(escrow): bounded admin setter for settlement limit with auth and events

[mimi-esc]

Summary

Adds an admin-guarded, bounded setter for the escrow's settlement-batch ceiling (set_settlement_limit) with a typed error, an event carrying old/new values, and a read view.

Approach

• Named bounds — MIN_SETTLEMENT_LIMIT / MAX_SETTLEMENT_LIMIT / DEFAULT_SETTLEMENT_LIMIT replace the hard-coded MAX_SETTLE_BATCH constant.
• Reused admin guard — set_settlement_limit calls load_escrow_require_admin, matching the existing admin-only setter pattern (set_protocol_fee_bps, set_storage_limit).
• Typed error — EscrowError::SettlementLimitOutOfRange (stable code 236) for out-of-range values; no leaked internals.
• Event — SettlementLimitUpdated { name, invoice_id, old_limit, new_limit }, emitted only when the stored value actually changes.
• Read views — get_settlement_limit() and the existing get_settlement_config() now expose the current ceiling.
• Wired into behavior — settle_batch now enforces the configured ceiling instead of the hard-coded MAX_SETTLE_BATCH (default stays 50, so existing behavior is unchanged until an admin tunes it).

Edge cases covered (tests)

• In-bounds set by admin → applied, event emitted.
• Out-of-bounds → rejected with SettlementLimitOutOfRange.
• Non-admin set → rejected.
• Read view reflects the change (individual getter + bundled config view).
• Event carries correct old/new values across consecutive changes.
• settle_batch enforces the configured limit.

Verification

• cargo fmt -p liquifact_escrow -- --check ✅
• cargo clippy -p liquifact_escrow --all-targets -- -D warnings ✅
• cargo test -p liquifact_escrow ✅ (7 new tests pass)
• cargo build --target wasm32v1-none --release -p liquifact_escrow ✅

Closes #1202

[mikewheeleer]

Hi @mimi-esc — this pull request currently has merge conflicts with the latest main branch. Please resolve the conflicts and push the updated branch so it can be merged. Thank you!