feat: Improve compiler diagnostics

[mark-koch]

This is the development branch for our new diagnostics infrastructure. Tracked by #535.

• #548
• #551
• #552
• #553

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 93.79310% with 81 lines in your changes missing coverage. Please review.

Project coverage is 92.45%. Comparing base (c142cc4) to head (09a6589).

Files with missing lines	Patch %	Lines
guppylang/checker/expr_checker.py	77.92%	17 Missing :warning:
guppylang/span.py	83.09%	12 Missing :warning:
guppylang/tys/parsing.py	56.52%	10 Missing :warning:
guppylang/checker/stmt_checker.py	76.47%	4 Missing :warning:
guppylang/compiler/expr_compiler.py	20.00%	4 Missing :warning:
guppylang/definition/function.py	71.42%	4 Missing :warning:
guppylang/prelude/_internal/checker.py	91.30%	4 Missing :warning:
guppylang/decorator.py	83.33%	3 Missing :warning:
guppylang/module.py	62.50%	3 Missing :warning:
guppylang/cfg/builder.py	89.47%	2 Missing :warning:
... and 11 more

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #547      +/-   ##
==========================================
+ Coverage   91.39%   92.45%   +1.06%     
==========================================
  Files          59       66       +7     
  Lines        6481     7464     +983     
==========================================
+ Hits         5923     6901     +978     
- Misses        558      563       +5     

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