Add snapshot test support for coverage implementation

[Porges]

Adds a test for srcview that exercises it against a real executable, as prep for #3362. This also adds test coverage for a lot of code we didn't have covered before.

Add a snapshot-based test to our coverage implementation. This adds coverage for a bunch of code which did not previously have it, and allows us to easily see that coverage is being generated as expected.

A fix was made to the recording code to remove the use of TargetAllowList as it was easy to misconfigure CoverageRecorder when using it. The use of TargetAllowList is now only a container struct in our generic coverage task.

[codecov-commenter]

Codecov Report

Merging #3368 (e28f16f) into main (d464e34) will increase coverage by 2.48%.
The diff coverage is 46.66%.

@@            Coverage Diff             @@
##             main    #3368      +/-   ##
==========================================
+ Coverage   32.21%   34.70%   +2.48%     
==========================================
  Files         302      302              
  Lines       36931    36917      -14     
==========================================
+ Hits        11897    12811     +914     
+ Misses      25034    24106     -928     

Files Changed	Coverage Δ
src/agent/coverage/src/allowlist.rs	89.79% <ø> (+11.03%)	⬆️
src/agent/coverage/src/binary.rs	66.66% <0.00%> (+12.06%)	⬆️
...c/agent/onefuzz-task/src/tasks/coverage/generic.rs	0.00% <0.00%> (ø)
src/agent/coverage/src/record/windows.rs	64.51% <42.85%> (+39.24%)	⬆️
src/agent/coverage/src/record.rs	78.89% <71.42%> (+3.44%)	⬆️
src/agent/coverage/src/record/linux.rs	64.28% <100.00%> (ø)
src/agent/coverage/src/source.rs	91.66% <100.00%> (+80.20%)	⬆️

... and 13 files with indirect coverage changes