refactor(test-tests): migrate precompile gas costs to fork.gas_costs()

[spencer-tb]

🗒️ Description

Migrate precompile gas costs from hardcoded Spec.* constants in test files to dynamic fork.gas_costs().G_PRECOMPILE_* lookups.

This is a pure refactor with no functional change, all test fixtures produce identical output (verified via fill + fixture hash comparison).

The benefit is maintainability: when EIP-7904 reprices precompiles (e.g., ECADD 150 to 314, BLS12_G1ADD 375 to 643, POINT_EVALUATION 50000 to 89363), only gas_costs.py and forks.py need updating instead of every test file.

GasCosts dataclass additions

New constants added with default=0, set per-fork:

Constant	Fork	Value
G_PRECOMPILE_ECRECOVER	Frontier	3000
G_PRECOMPILE_SHA256_BASE	Frontier	60
G_PRECOMPILE_SHA256_WORD	Frontier	12
G_PRECOMPILE_RIPEMD160_BASE	Frontier	600
G_PRECOMPILE_RIPEMD160_WORD	Frontier	120
G_PRECOMPILE_IDENTITY_BASE	Frontier	15
G_PRECOMPILE_IDENTITY_WORD	Frontier	3
G_PRECOMPILE_BLAKE2F_PER_ROUND	Istanbul	1
G_PRECOMPILE_POINT_EVALUATION	Cancun	50000
G_PRECOMPILE_BLS_G1ADD	Prague	375
G_PRECOMPILE_BLS_G1MUL	Prague	12000
G_PRECOMPILE_BLS_G1MAP	Prague	5500
G_PRECOMPILE_BLS_G2ADD	Prague	600
G_PRECOMPILE_BLS_G2MUL	Prague	22500
G_PRECOMPILE_BLS_G2MAP	Prague	23800
G_PRECOMPILE_BLS_PAIRING_BASE	Prague	37700
G_PRECOMPILE_BLS_PAIRING_PER_PAIR	Prague	32600
G_PRECOMPILE_P256VERIFY	Osaka	6900

Files migrated

• tests/cancun/eip4844_blobs/test_point_evaluation_precompile.py
• tests/cancun/eip4844_blobs/test_point_evaluation_precompile_gas.py
• tests/prague/eip2537_bls_12_381_precompiles/conftest.py + spec.py
• tests/osaka/eip7951_p256verify_precompiles/conftest.py + test_p256verify.py

Spec.* references in @pytest.mark.parametrize decorators are kept since fork is unavailable at module-load time. Beacon roots (Spec.BEACON_ROOTS_CALL_GAS) is skipped — it's a system contract, not a precompile.

🔗 Related Issues or PRs

Partially fixes #2049.

✅ Checklist

• All: Ran fast tox checks to avoid unnecessary CI fails, see also Code Standards and Enabling Pre-commit Checks:

  uvx tox -e static

• All: PR title adheres to the repo standard - it will be used as the squash commit message and should start type(scope):.
• All: Considered updating the online docs in the ./docs/ directory.
• All: Set appropriate labels for the changes (only maintainers can apply labels).

Cute Animal Picture

[spencer-tb]

I'm thinking of creating a similiar abstraction here called: precompile.gas_cost(fork, input_data)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.07%. Comparing base (a82b1f6) to head (7581447).
⚠️ Report is 6 commits behind head on forks/amsterdam.

Additional details and impacted files

@@               Coverage Diff                @@
##           forks/amsterdam    #2192   +/-   ##
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  Coverage            86.07%   86.07%           
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  Files                  599      599           
  Lines                39472    39472           
  Branches              3780     3780           
================================================
  Hits                 33977    33977           
  Misses                4862     4862           
  Partials               633      633           

Flag	Coverage Δ
unittests	86.07% <ø> (ø)

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[marioevz]

LGTM, thanks!