`AllAtOnceReducedFunctional` - initial time-parallel implementation

[JHopeCollins]

To merge into #3592

Parallelism implementation:

• observation stages distributed over ensemble
• context manager for recording the forward model and passing data between stages
• iterator to record each stage and set the observation

Context manager+iterator for taping each stage: https://github.com/firedrakeproject/4DVardrake/blob/2417d7cdff4a0a159ae8dcc9e12fb90d2382a67c/burgers/aaorf_4dvar_parallel.py#L250

[github-actions[bot]]

	Tests	Passed ✅	Skipped ⏭️	Failed ❌
Firedrake complex	8099 ran	6518 passed	1581 skipped	0 failed

[connorjward]

@JHopeCollins FYI I broke one of the runners today. Hence the failure. I will try and fix it tomorrow.

[github-actions[bot]]

	Tests	Passed ✅	Skipped ⏭️	Failed ❌
Firedrake real	8105 ran	7316 passed	789 skipped	0 failed

[JHopeCollins]

@JHopeCollins FYI I broke one of the runners today. Hence the failure. I will try and fix it tomorrow.

No problem. I think I also need to merge main to update the versions of some of the stuff in CI.