Descriptor/file organizational changes

[stevenengler]

Moved the Arc to within the PosixFile enum, and added the PosixFileRef and PosixFileRefMut types that hold a borrowed reference to the inner object.

This adds more boilerplate code, but is a lot more flexible when writing syscalls.

This is an updated version of #1083.

[codecov]

Codecov Report

Merging #1570 (3dad450) into main (3fe51e0) will decrease coverage by 0.06%.
The diff coverage is 100.00%.

❗ Current head 3dad450 differs from pull request most recent head b563fe9. Consider uploading reports for the commit b563fe9 to get more accurate results

@@            Coverage Diff             @@
##             main    #1570      +/-   ##
==========================================
- Coverage   52.73%   52.67%   -0.07%     
==========================================
  Files         141      141              
  Lines       21243    21237       -6     
  Branches     5375     5366       -9     
==========================================
- Hits        11203    11186      -17     
- Misses       7080     7088       +8     
- Partials     2960     2963       +3     

Flag	Coverage Δ
tests	52.67% <100.00%> (-0.07%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
src/main/host/descriptor/epoll.c	77.45% <100.00%> (ø)
src/main/routing/payload.c	61.97% <0.00%> (-1.41%)	⬇️
src/test/futex/test_futex.c	63.97% <0.00%> (-1.08%)	⬇️
src/lib/logger/rust_bindings/src/lib.rs	36.17% <0.00%> (-0.44%)	⬇️
src/main/host/descriptor/socket.c	65.64% <0.00%> (-0.39%)	⬇️
src/main/routing/topology.c	46.71% <0.00%> (-0.27%)	⬇️
src/test/tcp/test_tcp.c	33.95% <0.00%> (ø)
src/main/host/descriptor/file.c	29.47% <0.00%> (+0.18%)	⬆️
src/main/routing/packet.c	71.22% <0.00%> (+0.28%)	⬆️

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