6d7a/setup truststore for forked children

[6d7a]

Context

Closes #1508
1.54.0 introduced two TLS issues that caused backwards incompatibility:

• Python 3.14's multiprocessing behavior left processes with inconsistent TLS bundles
• Our Rust ureq client differed in its configuration from our python client, which caused issues for some users in self-hosted environments

What has been done

• we now make sure to use the system trust store in child processes
• our HTTP clients in Rust and Python now use similar configurations set by the same environment variables

PR check list

• As much as possible, the changes include tests (unit and/or functional)
• If the changes affect the end user (new feature, behavior change, bug fix) then the PR has a changelog entry (see doc/dev/getting-started.md). If the changes do not affect the end user, then the skip-changelog label has been added to the PR.

[codecov]

Codecov Report

❌ Patch coverage is 95.23810% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 94.49%. Comparing base (d9a60b9) to head (4e92269).
⚠️ Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
ggshield/cmd/utils/debug.py	75.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1545      +/-   ##
==========================================
- Coverage   94.50%   94.49%   -0.01%     
==========================================
  Files         200      201       +1     
  Lines       12767    12780      +13     
==========================================
+ Hits        12065    12077      +12     
- Misses        702      703       +1     

Flag	Coverage Δ
unittests	94.49% <95.23%> (-0.01%)	⬇️

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