Refactor out use of anyhow

[algesten]

This is part of work spanning all the webrtc crates: webrtc-rs/webrtc#106

This crate had multiple error enum types. Rather than converting between them, this PR merges them all into one unified error.

[codecov]

Codecov Report

Merging #12 (bad3aff) into main (5881f90) will decrease coverage by 0.26%.
The diff coverage is 6.12%.

@@            Coverage Diff             @@
##             main      #12      +/-   ##
==========================================
- Coverage   45.98%   45.72%   -0.27%     
==========================================
  Files          30       27       -3     
  Lines        3179     3191      +12     
  Branches     1379     1378       -1     
==========================================
- Hits         1462     1459       -3     
- Misses        286      303      +17     
+ Partials     1431     1429       -2     

Impacted Files	Coverage Δ
src/buffer/buffer_test.rs	25.77% <0.00%> (ø)
src/conn/conn_udp_listener.rs	61.87% <0.00%> (ø)
src/conn/conn_udp_listener_test.rs	41.04% <0.00%> (-0.14%)	⬇️
src/lib.rs	12.50% <0.00%> (-87.50%)	⬇️
src/vnet/chunk/chunk_test.rs	43.58% <ø> (ø)
src/vnet/chunk_queue/chunk_queue_test.rs	24.13% <ø> (ø)
src/vnet/conn/conn_test.rs	53.38% <0.00%> (+0.39%)	⬆️
src/vnet/interface.rs	66.66% <0.00%> (ø)
src/vnet/net/net_test.rs	37.37% <0.00%> (ø)
src/vnet/router/router_test.rs	55.53% <0.00%> (ø)
... and 3 more

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[algesten]

Marking this as draft since merging it would become a blocker for any other webrtc-rs work that affects the util crate.

I need to sort out dependent crates simultaneously with this one.