Feat: Do Cerebellum per lobules

[arnaudon]

This PR has three things:

• option to save meshes locally, and reuse them. To later use these meshes, or faster debugging
• option to compute distances following vector fields, instead of straight ray-tracing (crucial for cerebellum, could be useful for other regions)
• option to bypass ultralizer and use simple marching cube algo from trimesh to avoid smoothing artifacts
• better handling of cerebellum, by doing ph per lobules, and using curved ray-tracing

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 40.33613% with 71 lines in your changes are missing coverage. Please review.

Project coverage is 70.38%. Comparing base (11e099b) to head (7bb6f40).

Files	Patch %	Lines
atlas_placement_hints/layered_atlas.py	14.28%	36 Missing :warning:
...s_placement_hints/distances/distances_to_meshes.py	42.00%	29 Missing :warning:
...lacement_hints/distances/create_watertight_mesh.py	77.77%	6 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #22 +/- ## ========================================== - Coverage 79.91% 70.38% -9.53% ========================================== Files 9 9 Lines 453 547 +94 ========================================== + Hits 362 385 +23 - Misses 91 162 +71 ``` | [Flag](https://app.codecov.io/gh/BlueBrain/atlas-placement-hints/pull/22/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=BlueBrain) | Coverage Δ | | |---|---|---| | [pytest](https://app.codecov.io/gh/BlueBrain/atlas-placement-hints/pull/22/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=BlueBrain) | `70.38% <40.33%> (-9.53%)` | :arrow_down: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=BlueBrain#carryforward-flags-in-the-pull-request-comment) to find out more.

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