fix: remove accidental type monomorphism in Id.run_seqLeft

[eric-wieser]

This PR fixes Id.run_seqLeft and Id.run_seqRight to apply when the two monad results are different.

[eric-wieser]

changelog-library

[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 5c685465bd442d278f26997393464bcd8c87062b --onto cfa8c5a036d6990635c6ec50b02d0e806995cec3. You can force Mathlib CI using the force-mathlib-ci label. (2026-03-17 00:37:22)

[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 5c685465bd442d278f26997393464bcd8c87062b --onto cfa8c5a036d6990635c6ec50b02d0e806995cec3. You can force reference manual CI using the force-manual-ci label. (2026-03-17 00:37:24)

[TwoFX]

Thanks!