feat(test-fixtures): resolve implicit transaction test gas limits

[danceratopz]

Description

StateTest and BlockchainTest resolve an omitted transaction gas limit before signing, but TransactionTest previously signed the transaction directly. This forced transaction tests to provide an otherwise arbitrary gas limit or fail with gas_limit must be set to sign a transaction.

This PR resolves omitted limits through the shared Transaction.with_gas_limit(...) behavior before signing. It uses the configured default block gas budget, preserves explicit limits, applies Osaka's transaction gas cap, and retains Amsterdam's state gas reservoir behavior.

The existing transaction tests now omit gas limits when gas is unrelated to the behavior under test. This keeps them useful as examples of the intended TransactionTest API. The explicit limit in the raw RLP source helper remains because that helper signs and serializes its transaction before the filler or execute pipeline can resolve an implicit limit.

The test intentions and expected results remain unchanged. The refactored tests still exercise the same nonce overflow, authorization-format, and RLP-validation cases with the same expected exceptions. Their serialized bytes and signatures intentionally change because the framework now supplies the gas limit.

Execute mode remains supported. TransactionPost.prepare_transactions() resolves omitted limits from the live environment and fork configuration before calculating balances and signing transactions.

Stack

This is the second PR in a three-PR stack:

1. feat(spec-specs): expose state-independent transaction validation #3492 — Expose state-independent transaction validation.
2. feat(test-fixtures): resolve implicit transaction test gas limits #3493 — Resolve implicit transaction test gas limits (this PR).
3. feat(spec-tests): validate transaction test fixtures against EELS #3494 — Validate transaction test fixtures with EELS.

Related Issues or PRs

Fixes #3489.

Testing

• Added coverage for omitted and explicit limits, Osaka's cap, and Amsterdam's state gas reservoir behavior.
• Filled the three affected test modules: 1,178 tests passed.
• Compared fixtures before and after with hasher compare: 124 transaction fixture hashes changed because the gas limit and signature changed; none of the 1,178 expected result values or exceptions changed.
• Repeated the comparison for Amsterdam: 56 transaction fixture hashes changed and no expected results changed.
• Collected the affected modules under execute mode for Amsterdam and exercised preparation and signing for the nonce-overflow, invalid type-4, and raw-RLP patterns.
• just static
• just test-tests
• just json-loader on the restacked feat(spec-tests): validate transaction test fixtures against EELS #3494 branch

Checklist

• Ran fast static checks to avoid CI fails, see Code Standards and Verifying Changes: just static
• PR title has the form <type>(<area>): <title>, where <type> and <area> match the applied labels.

Cute Animal Picture

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.90%. Comparing base (f7fbf65) to head (73023cf).

Additional details and impacted files

@@                                 Coverage Diff                                 @@
##           experiments/expose-state-independent-tx-validation    #3493   +/-   ##
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  Lines                                                   36938    36938           
  Branches                                                 3330     3330           
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  Hits                                                    34688    34688           
  Misses                                                   1569     1569           
  Partials                                                  681      681           

Flag	Coverage Δ
unittests	93.90% <ø> (ø)

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