Test Ignite handling of decimal type with negative scale

[joseguzman1337]

Summary

Adds a unit test to TestIgniteClient that verifies IgniteClient.toColumnMapping() correctly maps decimal(p, -s) (negative scale) to decimal(p+s, 0), as implemented in the existing comment in IgniteClient.java:

precision = precision + max(-decimalDigits, 0); // Map decimal(p, -s) (negative scale) to decimal(p+s, 0).

The test uses JdbcTypeHandle with precision=5, scale=-3 and asserts the result is DECIMAL(8, 0).

Closes #28416

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