Replace Issue in STIssue with Asset. STIssue with MPTIssue is only used in MPT tests.
Will be used in Vault and in transactions with STIssue fields once MPT is integrated into DEX.
* Rename ASSERT to XRPL_ASSERT
* Upgrade to Anthithesis SDK 0.4.4, and use new 0.4.4 features
* automatic cast to bool, like assert
* Add instrumentation workflow to verify build with instrumentation enabled
* Copy Antithesis SDK version 0.4.0 to directory external/
* Add build option `voidstar` to enable instrumentation with Antithesis SDK
* Define instrumentation macros ASSERT and UNREACHABLE in terms of regular C assert
* Replace asserts with named ASSERT or UNREACHABLE
* Add UNREACHABLE to LogicError
* Document instrumentation macros in CONTRIBUTING.md
