test(sql-parser): add multi-row column-explicit INSERT negative literal test coverage (#4659)

[Tyagiquamar]

Summary

Adds explicit test cases verifying multi-row and column-explicit \INSERT\ statements containing negative numeric literals (e.g. \INSERT INTO t (a, b) VALUES (-1, -2), (+3, -4.5)) are correctly handled by \spacetimedb-sql-parser.

Closes #4659

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[Tyagiquamar]

Hi, just following up on this when you get a chance. The branch is up to date and checks are green. If it looks good from your side, it should be ready to merge. Happy to make any changes if needed. Thanks!