test(js): implement comprehensive test suite for BurnChecked instruction

[raushan728]

Summary
This pull request introduces a dedicated test suite for the BurnChecked instruction within the JavaScript SDK (clients/js). The suite provides full coverage for the instruction, ensuring that both expected behavior and error conditions are strictly validated in accordance with the SPL Token program logic.

Technical Changes

• New Test File: Created clients/js/test/burnChecked.test.ts.
• Test Framework: Utilized the Ava testing framework as per repository standards.
• Infrastructure: Leveraged project-specific setup helpers including createMint, createTokenWithAmount, and signAndSendTransaction to ensure environment consistency.

Test Scenarios Covered

Success Path Validations:

• Standard Burn: Validates that burning a specified amount with correct decimals accurately updates the account balance and mint supply.
• Exhaustive Burn: Confirms that burning the entire account balance results in a zero-balance state.
• Delegated Burn: Verifies that an authorized delegate can perform burns and that the delegatedAmount updates appropriately.
• Mint Supply Consistency: Confirms that total supply reflects burns accurately across multiple token accounts.
• Edge Case - Zero Amount: Ensures that burning 0 tokens is handled as a valid, no-op transaction.
• Precision Scaling: Validates the instruction across different decimal scales, specifically testing 0 (integer) and 18 (high-precision) decimals.

Failure Mode Validations:

• Decimal Mismatch: Ensures the transaction is rejected when instruction decimals do not match the mint's configuration.
• Insufficient Funds: Validates rejection when the burn amount exceeds the available account balance.
• Signature Verification: Confirms that instructions fail if the required authority is not a signer.
• Delegation Limits: Ensures a delegate cannot burn tokens beyond the amount approved by the owner.

Technical Verification

• Build Status: Verified via pnpm build in the clients/js directory.
• Local Validator: Tests were executed against a local solana-test-validator.
• Execution Command: npx ava dist/test/burnChecked.test.js
• Results: 10 out of 10 tests passed successfully.

Checklist

• Code adheres to the architectural patterns of the repository (pipe, signers, etc.).
• All new tests have been verified to pass on a local validator.
• Self-review performed to ensure no redundant code or unused imports are present.
• Documentation and comments follow the established project style.