fix: allow negative gas refund propagation

[abmcar]

1. Does this PR affect any open issues?(Y/N) and add issue references (e.g. "fix #123", "re #123".):

• N
• Y

2. What is the scope of this PR (e.g. component or file name):

3. Provide a description of the PR(e.g. more details, effects, motivations or doc link):

• Affects user behaviors
• Contains CI/CD configuration changes
• Contains documentation changes
• Contains experimental features
• Performance regression: Consumes more CPU
• Performance regression: Consumes more Memory
• Other

4. Are there any breaking changes?(Y/N) and describe the breaking changes(e.g. more details, motivations or doc link):

• N
• Y

5. Are there test cases for these changes?(Y/N) select and add more details, references or doc links:

• Unit test
• Integration test
• Benchmark (add benchmark stats below)
• Manual test (add detailed scripts or steps below)
• Other

6. Release note

None

[Copilot]

Pull request overview

This PR updates EVM gas refund accounting to correctly propagate negative refund deltas (e.g., refund cancellations from net SSTORE accounting and subcall refund adjustments), avoiding incorrect unsigned wrap/ignoring negative values.

Changes:

• Switch EVMInstance::GasRefund and related APIs from uint64_t to int64_t.
• Update interpreter frame refund snapshots to int64_t to preserve correct rollback semantics.
• Always propagate Result.gas_refund from subcalls (CREATE/CALL paths), including negative values.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
src/runtime/evm_instance.h	Make gas refund storage and accessors signed (int64_t) to support negative refund deltas.
src/evm/opcode_handlers.cpp	Clarify that subcall refund deltas may be negative when accumulating at instance level.
src/evm/interpreter.h	Store gas refund snapshots as int64_t for correct restore behavior.
src/compiler/evm_frontend/evm_imported.cpp	Propagate subcall gas_refund unconditionally (including negative values) in JIT-imported call/create helpers.

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