feat/add multi-operation transaction decoding

[EmmyKay0026]

Description

This PR adds full multi-operation transaction decoding support.

Grat now processes every operation in a transaction envelope instead of assuming the transaction contains a single InvokeHostFunction operation. Transactions containing classic Stellar operations and multiple Soroban operations now produce a separate diagnostic report for each operation.

How It Was Done

• Added envelope-wide operation iteration for V0, V1, and fee-bump transactions.
• Preserved the original operation index and order in all generated reports.
• Added operation-specific decoding:
  • Soroban contract calls use FunctionCallDecoder.
  • Classic Stellar and other Soroban operations use structured XDR extraction.
• Matched each operation with its corresponding XDR result.
• Added support for transaction-level failures and operations that were not executed.
• Distinguished operation failures from successful operations rolled back by atomic transaction failure.
• Associated diagnostic and contract events with their relevant Soroban operation where possible.
• Added clear Operation N/Total labels and operation metadata to diagnostic reports.
• Added validation for out-of-range operation filters.
• Added regression tests for classic operation success, missing results, and result-type mismatches.

Issues Encountered (If Any)

The local Rust compilation environment did not include gcc.exe, which is required to build the ring dependency under the configured GNU toolchain.

The implementation was kept strictly within the requested decoder files.

Related Issue

Closes #392

How It Was Tested

• Added focused unit tests for:

  • Successful classic Stellar operations.
  • Missing operation results.
  • Mismatched operation and result types.

• Ran cargo fmt --all -- --check successfully.

• Ran git diff --check successfully.

• Confirmed that only the requested decoder files were modified.

• Full Cargo tests should be rerun in an environment with MinGW/GCC installed:

  cargo test -p grat-core --lib

Screenshots / Video (If Applicable)

Not applicable. This PR only changes core transaction decoding behavior.

[coderabbitai]

Important

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Review profile: CHILL

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Run ID: 382372b7-d1f9-434f-b3b4-b2e8dda64904

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[codeZe-us]

PR reviewed and merged