fix: correct swapped operands in Std.Time subtraction instances

[jessealama]

This PR fixes the HSub PlainTime Duration instance, which had its operands reversed: it computed duration - time instead of time - duration. For example, subtracting 2 minutes from time("13:02:01") would give time("10:57:59") rather than the expected time("13:00:01"). We also noticed that HSub PlainDateTime Millisecond.Offset is similarly affected.

Closes #12918

[mathlib-lean-pr-testing]

Mathlib CI status (docs):

• ❗ Batteries/Mathlib CI will not be attempted unless your PR branches off the nightly-with-mathlib branch. Try git rebase c2d4079193fa62cbd177059d9022c7a7ae097c42 --onto e8048291010c815d0d30926924e7ad7afc18b1c0. You can force Mathlib CI using the force-mathlib-ci label. (2026-03-14 15:20:19)

[leanprover-bot]

Reference manual CI status:

• ❗ Reference manual CI will not be attempted unless your PR branches off the nightly-with-manual branch. Try git rebase c2d4079193fa62cbd177059d9022c7a7ae097c42 --onto 47b3be05247c1d749f7031c06405ddc86daa4b09. You can force reference manual CI using the force-manual-ci label. (2026-03-14 15:20:21)
• ❗ Reference manual CI can not be attempted yet, as the nightly-testing-2026-03-09 tag does not exist there yet. We will retry when you push more commits. If you rebase your branch onto nightly-with-manual, reference manual CI should run now. You can force reference manual CI using the force-manual-ci label. (2026-03-14 22:12:22)

[mathlib-lean-pr-testing]

Mathlib CI status (docs):

• ✅ Mathlib branch lean-pr-testing-12919 has successfully built against this PR. (2026-03-14 23:05:23) View Log

[TwoFX]

Thanks!