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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