Preserve collection claims with historical numeric metadata

[rohenaz]

Collection items with historical "mintNumber":"42" metadata lost their otherwise valid collection ID because the parser decoded required and optional fields together. Parse the collection claim independently and accept canonical nonnegative display integers as numbers or legacy strings, bounded by the host integer and JavaScript safe-integer range. Invalid optional metadata stays available as raw data and does not erase the claim.

Adds regressions for malformed fields and the existing Musashi transaction fixture 34adf92c…f701f9. This preserves claim parsing; it does not add collection-issuer matching or turn overlay admission into verified membership.

Validation: go test ./pkg/collection ./pkg/parse, gofmt and git diff --check pass. Related proposal: opldotdev/BRCs#13.

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