feat: add E2E tests for EIP-7951 (secp256r1 P-256 verify precompile)

[libotony]

Summary

• Add tests/eip7951 package with 5 E2E tests covering the secp256r1 (P-256) signature verification precompile added at the INTERSTELLAR fork (implement eip-7951: add secp256r1 verify precompile thor#1602)
• Tests cover pre/post-fork behavior, gas cost, wrong-length guard, and a full on-chain contract call path

Tests Added

• TestEIP7951_ValidSignature — direct call to 0x0100 with valid P-256 sig; pre-fork: empty output, post-fork: returns 32-byte 1
• TestEIP7951_InvalidSignature — corrupted s value; post-fork: empty output, no revert
• TestEIP7951_GasCost — verifies P256VerifyGas = 6900 post-fork, 0 pre-fork
• TestEIP7951_WrongInputLength — 100-byte input (not 160); post-fork: empty output, no revert
• TestEIP7951_ContractCall — deploys a minimal EVM proxy contract that calls the precompile via staticcall; valid sig → returns 1, invalid sig → returns 0

Test Plan

• All 5 tests pass via make test
• Pre-fork cases return empty output as expected
• Post-fork valid sig returns 32-byte big-endian 1
• Gas assertion = 6900
• Contract proxy deployment and call both verified on-chain
• go vet passes

[BenderVeChain]

LGTM. Bytecode verified, all five test cases are correct, and the updated WrongInputLength test now covers both too-short (100 bytes) and too-long (192 bytes) inputs with explicit gas assertions (GasUsed=6900). No outstanding issues.