[builder] improve unit tests

[bkmartinjr]

Changes:

• Add additional unit tests and fix one small bug found by those new tests
• Enable coverage to be collected more easily, by running tests in a single process (i.e., change to Dask cluster config for tests)
• Run with and without Numba JIT, to fully capture coverage and continue testing in the as-used mode (numba enabled).
• Reduce memory budget for consolidation to allow testing in small instances (does not affect normal Census build)
• Additional unit tests to cover float precision reduction in more detail
• Update to latest tiledbsoma version
• Fix bug in HVG uncovered by enabling categoricals in the Census build

This should significantly increase Builder coverage (some due to new tests, some due to more accurate code coverage)

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 98.37838% with 3 lines in your changes are missing coverage. Please review.

Project coverage is 91.12%. Comparing base (c6cf312) to head (066d8ec). Report is 2 commits behind head on main.

Files	Patch %	Lines
tools/cellxgene_census_builder/tests/conftest.py	83.33%	2 Missing :warning:
...src/cellxgene_census_builder/build_soma/anndata.py	90.90%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #1067 +/- ## ========================================== + Coverage 82.34% 91.12% +8.78% ========================================== Files 74 76 +2 Lines 5714 5872 +158 ========================================== + Hits 4705 5351 +646 + Misses 1009 521 -488 ``` | [Flag](https://app.codecov.io/gh/chanzuckerberg/cellxgene-census/pull/1067/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=chanzuckerberg) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/chanzuckerberg/cellxgene-census/pull/1067/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=chanzuckerberg) | `91.12% <98.37%> (+8.78%)` | :arrow_up: | 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=chanzuckerberg#carryforward-flags-in-the-pull-request-comment) to find out more.

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[bkmartinjr]

@ebezzi @prathapsridharan - given the HVG fix in this PR, you may want to consider pushing a patch release once this lands.