refactor: split isolation.rs into files

[n0toose]

This is a form of preparation for the introduction of additional security-related measures, which may be best to implement in separate files.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 71.55%. Comparing base (cb1371f) to head (c9535e6).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #814   +/-   ##
=======================================
  Coverage   71.55%   71.55%           
=======================================
  Files          21       22    +1     
  Lines        3041     3041           
=======================================
  Hits         2176     2176           
  Misses        865      865           

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[jounathaen]

👍

[n0toose]

not sure if i got the write access on purpose - but given you attempted to merge this and that the conflict was only really about removing tempdir's dependencies from filemap.rs (and because the tests pass), i'm assuming that it's OK if i merge this myself either way