Extend Wasm execution tracing to host calls, storage, objects, and contract calls

[bbyalcinkaya]

This PR extends the existing instruction-level execution tracing (tracing.md) to cover the higher-level events: host function calls, storage reads/writes, host object allocation, and the start and end of every contract call, including a snapshot of the callee's storage before it runs.

Added traces

• Host calls (traceHostCall): every host function invocation logs its module/function name and the current locals. hostCall was changed from Instr to HelperInstr so it's no longer picked up by the generic per-instruction tracer, and is logged once via this dedicated hook instead.
• Storage (trace-putContractData/trace-delContractData): logs the contract, storage type (instance, persistent, or temporary), and key/value for every storage write and delete.
• Host objects (trace-addObject): logs the ScVal value and the index a new host object is about to be created.
• Contract calls (trace-callContract / trace-endWasm / trace-endWasm-error) — new in this PR:
  • trace-callContract logs the start of every contract call: caller, callee, function name, arguments (List of ScVal), call depth, and the callee's full storage (instance + persistent/temporary, each tagged with its durability) as it stands before the call runs.
  • trace-endWasm / trace-endWasm-error log the end of every contract call: success/failure, call depth, and the resolved return value or Error.
  • Both cover the outermost invocation (e.g. via callTx) as well as every nested call/try_call sub-call, since all contract calls funnel through callContract/#endWasm regardless of how they were initiated.

Design notes

• trace-callContract/trace-endWasm/trace-endWasm-error duplicate the state transition of their corresponding base rules in soroban.md/switch.md (rather than appending #resetAlreadyTraced and requeuing).
• The now-redundant <logging> cell was removed; its only use (logging callContract invocations) is superseded by trace-callContract.
• Added doc comments to callContract/callContractAux/mkCall in soroban.md explaining the three-command call-setup handoff, since tracing now duplicates part of it.

Testing

Added three tracing-specific tests to src/tests/integration/test_integration.py that run .wast fixtures with tracing and assert on the resulting JSON records:

• test_tracing_call_contract_and_end_wasm — checks callContract/endWasm are each logged once per call, depths agree between a call's start/end and increase for the nested call, and args/result resolve correctly (call_add.wast).
• test_tracing_end_wasm_error — checks a panicking call's endWasm is logged as a failure with the trap's Error, and that tracing continues correctly afterward (increment_panic.wast).
• test_tracing_call_contract_storage — checks each callContract's storage snapshot reflects the previous call's writes, and that the individual trace-putContractData/trace-delContractData writes are logged in order (put, del, put) with the right contract, durability, and args (storage.wast).

[RaoulSchaffranek]

LGTM. Let's just make sure that the JSON format for host interactions is properly documented, an example trace would be highly beneficial.