docs: adding some docs to the tce-proxy

[dvdplm]

Adding some docs here and there to prove to myself that
I have understood the code.

[codecov]

Codecov Report

Attention: 4 lines in your changes are missing coverage. Please review.

Comparison is base (e05cdfb) 60.44% compared to head (d26ac0e) 60.42%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #316      +/-   ##
==========================================
- Coverage   60.44%   60.42%   -0.02%     
==========================================
  Files         225      225              
  Lines       11976    11976              
==========================================
- Hits         7239     7237       -2     
- Misses       4737     4739       +2     

Files	Coverage Δ
crates/topos-tce-proxy/src/worker.rs	48.54% <100.00%> (ø)
crates/topos-tce-proxy/tests/tce_tests.rs	44.82% <ø> (ø)
crates/topos-sequencer/src/app_context.rs	0.00% <0.00%> (ø)
crates/topos-sequencer/src/lib.rs	0.00% <0.00%> (ø)
crates/topos-tce-proxy/src/lib.rs	66.66% <0.00%> (ø)

... and 3 files with indirect coverage changes

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