Use upstream EIP-7951 test vectors for P256VERIFY tests

[snissn]

Context

• builtin-actors PR EIP-7951 (RIP-7212-compatible): secp256r1 P256VERIFY precompile #1708 adds the secp256r1 (P-256) P256VERIFY precompile (0x0100, EIP-7951 / RIP-7212 interface).
• Current tests use embedded vectors sourced from daimo-eth/p256-verifier.

Request

• Vendor the upstream EIP-7951 test vector set (test-vectors.json) into the builtin-actors repo.
• Update/add tests to consume the vendored JSON and validate P256VERIFY behavior against it.

Notes

• Upstream vectors: https://eips.ethereum.org/assets/eip-7951/test-vectors.json
• PR: EIP-7951 (RIP-7212-compatible): secp256r1 P256VERIFY precompile #1708

Acceptance criteria

• Vendored JSON is checked in with a short provenance note (source URL + date/commit if available).
• Tests iterate vectors (optionally filtering NoBenchmark) and assert output semantics (32-byte 0x..01 on success, empty on failure) and non-revert behavior.
• CI runtime remains reasonable (sampling/filtering is OK if needed).