Re-enable disabled tests in ContractFunctionParametersTest and MockingTest

Two unit tests are disabled with a bare `@Disabled` and no explanation:

- `ContractFunctionParametersTest.bigIntChecks()` ("BigInteger checks") — `sdk/src/test/java/com/hedera/hashgraph/sdk/ContractFunctionParametersTest.java:517`
- `MockingTest.defaultMaxQueryPaymentTest()` ("Client.setDefaultMaxQueryPayment() functions correctly") — `sdk/src/test/java/com/hedera/hashgraph/sdk/MockingTest.java:649`

Both cover behavior we want regression protection on: int256 boundary handling in `ContractFunctionParameters`, and client-level default query payment limits.

Scope: run each locally, dig up why it was turned off (git blame the `@Disabled` line), then either fix the underlying problem and re-enable, or keep it disabled with a `@Disabled("reason")` string plus a linked issue so the gap is documented instead of silent.

Start with sdk/src/test/java/com/hedera/hashgraph/sdk/ContractFunctionParametersTest.java:517 and MockingTest.java:649. Run bigIntChecks() and defaultMaxQueryPaymentTest(), then use git blame on each @Disabled line to find why it was added. Done means either fixing the underlying problem and re-enabling both tests, or adding specific reasons and linked issues to document any remaining gap.

Written by the indexing model from the issue text.