improve the building system

[fnikolai]

Description

1. Move testenv from test/material to deploy.
2. Decide whether to change /etc/hosts on every testenv_init or just document it.
3. Fix caching layer in Dockerfile

Related Issues

#1324

Checklist

• Is this code covered by new or existing unit tests or integration tests?
• Did you run make test successfully?
• Do new classes, functions, methods and parameters all have docstrings?
• Were existing docstrings updated, if necessary?
• Was external documentation updated, if necessary?

Additional Notes or Comments

[codecov-commenter]

Codecov Report

Attention: 218 lines in your changes are missing coverage. Please review.

Comparison is base (34830a7) 80.33% compared to head (831c9d2) 79.46%.
Report is 72 commits behind head on main.

Files	Patch %	Lines
superduperdb/components/stack.py	0.00%	65 Missing ⚠️
superduperdb/backends/ibis/query.py	52.17%	44 Missing ⚠️
superduperdb/server/app.py	67.56%	24 Missing ⚠️
superduperdb/cli/stack.py	0.00%	9 Missing ⚠️
superduperdb/vector_search/interface.py	75.67%	9 Missing ⚠️
superduperdb/jobs/tasks.py	0.00%	8 Missing ⚠️
superduperdb/base/build.py	57.14%	6 Missing ⚠️
superduperdb/cdc/cdc.py	62.50%	6 Missing ⚠️
superduperdb/base/datalayer.py	83.33%	5 Missing ⚠️
superduperdb/cli/serve.py	54.54%	5 Missing ⚠️
... and 16 more

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1326      +/-   ##
==========================================
- Coverage   80.33%   79.46%   -0.88%     
==========================================
  Files          95      100       +5     
  Lines        6602     6822     +220     
==========================================
+ Hits         5304     5421     +117     
- Misses       1298     1401     +103     

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