feat: allow meshes to be exported

[xgui3783]

fixes https://github.com/FZJ-INM1-BDA/siibra-python/issues/396

[codecov-commenter]

Codecov Report

Attention: 1281 lines in your changes are missing coverage. Please review.

Comparison is base (5a0e6b3) 36.81% compared to head (b6fd7fa) 50.66%. Report is 297 commits behind head on main.

Files	Patch %	Lines
siibra/volumes/volume.py	44.13%	119 Missing :warning:
siibra/features/feature.py	48.09%	109 Missing :warning:
siibra/explorer/url.py	0.00%	107 Missing :warning:
siibra/volumes/parcellationmap.py	18.25%	103 Missing :warning:
siibra/core/region.py	62.34%	90 Missing :warning:
...bra/features/connectivity/regional_connectivity.py	25.97%	57 Missing :warning:
siibra/retrieval/datasets.py	51.81%	53 Missing :warning:
siibra/explorer/util.py	0.00%	51 Missing :warning:
...a/features/tabular/regional_timeseries_activity.py	25.00%	48 Missing :warning:
siibra/configuration/factory.py	54.34%	42 Missing :warning:
... and 38 more

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Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #516 +/- ## =========================================== + Coverage 36.81% 50.66% +13.84% =========================================== Files 61 71 +10 Lines 5421 6512 +1091 =========================================== + Hits 1996 3299 +1303 + Misses 3425 3213 -212 ```

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[AhmetNSimsek]

@dickscheid is reluctant to add another requirement at the moment. We should discuss mesh support of siibra-python in general and choose a lane accordingly. This could very well be trimesh.

[AhmetNSimsek]

At the dev meeting on 25.01.2024, it is decided against this PR and in favor of #554 .