fix(#190): rename internal _settle params to avoid shadowing

[Mkalbani]

Summary

Renames the internal _settle function parameters from beneficiary / amount to _beneficiary / _amount (underscore-prefix convention) to eliminate any potential shadowing of inherited declarations flagged during audit.

Changes

• contracts/TruthBountyClaims.sol — Renamed _settle params and updated internal references. Call sites (settleClaim, settleClaimsBatch) untouched — args are positional.
• test/TruthBountyClaims.test.ts — Added unit test asserting single and batch paths emit the correct ClaimSettled args and balances after the rename.

Why

• Audit Ref CO-190 identified parameter shadowing risk inside _settle.
• Underscore-prefix is the standard Solidity/OpenZeppelin convention for internal function params and disambiguates them from any state-variable or inherited-scope identifiers.
• Behavior, ABI, and storage layout are unchanged → no regressions.

Acceptance Criteria

• Implementation functional
• Tests added (single + batch ClaimSettled args)
• No regressions (ABI/storage unchanged)

Security / Integrity

• Purely a renamimg refactor; no logic or access-control changes. No new trust assumptions.

Risk

• Low. Internal-only rename; callers are unaffected.

References

• Internal: Ref #CO-190
• Branch: feat/audit-190-shadowing-settle

closes #190