fix(engine): match enum keys case-insensitively when no exact key matches

[kuzdogan]

Problem

The enum formatter looks up the field value with an exact string match. A bool argument renders as "true" or "false", but a descriptor may spell the enum keys "True" and "False". The lookup then misses and the raw value is shown.

Seen in the ERC-7730 registry CI on the PR that adds two Sourcify-found deployments to the Flying Tulip pFT NFT descriptor, ethereum/clear-signing-erc7730-registry#2926 (job log):

Approve pFT operator — field value at [1] "Access rights": expected "Grant all", got "true"

The descriptor has:

"enums": { "rights": { "True": "Grant all", "False": "Deny all" } }

and formats setApprovalForAll(address operator, bool approved)'s approved with "format": "enum", "$ref": "$.metadata.enums.rights".

The ERC-7730 schema only says that enum keys are "the field values". It does not fix a spelling for booleans, and the registry has both: ekubo/calldata-MEVCaptureRouter.json uses "true"/"false", flyingtulip/calldata-PftNft.json used "True"/"False". @ethereum-sourcify/clear-signing resolves both, because its resolveEnumLabel falls back to a case-insensitive key scan after an exact miss.

Change

• New lookup_enum_label in engine.rs. It resolves the enum by enumPath (v1) or $ref (v2), tries an exact key match first, and only then compares keys with eq_ignore_ascii_case.
• format_enum (calldata) and the FieldFormat::Enum arm in eip712.rs both call it. This removes the duplicated lookup code in the two files.
• Unit tests: bool values match True/False keys, an exact key still wins over a case-insensitive one, enumPath works, and unknown enums or keys still return None so the raw value is rendered as before.

Integer enums are unaffected: their keys are decimal strings, which have no case.

Testing

cargo fmt --check passes and the new unit tests pass:

test engine::tests::bool_argument_renders_as_lowercase_and_still_matches_capitalized_enum_key ... ok
test engine::tests::enum_lookup_prefers_exact_key_and_supports_enum_path ... ok
test engine::tests::enum_lookup_returns_none_for_unknown_enum_or_key ... ok
test engine::tests::enum_lookup_matches_bool_keys_case_insensitively ... ok

I did not run the full suite or clippy locally, so please rely on CI for those.

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