coexec: normalize the timestamp subtraction like postgres

[yuzefovich]

This commit fixes an oversight of #56667 (which fixed the normalization
of the timestamp subtraction) where we forgot to update the vectorized
code path as well. The regression tests added in that PR happened to be
complex enough so that the vectorized engine would fall back to wrapping
a row-by-row processor, so they didn't catch this.

Fixes: #83094.

Release note (bug fix): CockroachDB previously would not normalize
timestamp/timestamptz - timestamp/timestamptz like Postgres does in
some cases (depending on the query), and this is now fixed.

[cockroach-teamcity]

This change is 

[DrewKimball]

Reviewable status: complete! 1 of 0 LGTMs obtained (waiting on @msirek)

[yuzefovich]

TFTRs!

bors r+

[craig]

Build failed (retrying...):

• GitHub CI (Cockroach)

[craig]

Build succeeded:

• GitHub CI (Cockroach)

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