release-25.2: roachtest: fix unsortedMatricesDiffWithFloatComp helper for numerics

[yuzefovich]

Backport 1/1 commits from #147051 on behalf of @yuzefovich.

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This commit is similar in spirit to 261cae9. We use T_numeric and T__numeric oids for decimals and decimal arrays, respectively. These oids have "NUMERIC" and "_NUMERIC" names in lib/pq when stringified, so we need to teach our custom logic for ignoring trailizing zeroes to also apply whenever it sees the numeric column types.

Fixes: #146524.

Release note: None

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Release justification: test-only change.

[blathers-crl]

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[cockroach-teamcity]

This change is