documentation: use generic lexer infrastructure in Toy parser

[superlopuh]

Just to make sure that it really is generic, here's the port of Toy's lexing to the new structure. Up next: generic base parser infrastructure.

Note stacked PR.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 90.40%. Comparing base (09f495a) to head (328f062).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3593   +/-   ##
=======================================
  Coverage   90.39%   90.40%           
=======================================
  Files         470      470           
  Lines       59123    59126    +3     
  Branches     5616     5610    -6     
=======================================
+ Hits        53443    53451    +8     
+ Misses       4233     4232    -1     
+ Partials     1447     1443    -4     

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[compor]

that's great