feat: Update statement checker to use new diagnostics

[mark-koch]

Closes #540

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 95.23810% with 2 lines in your changes missing coverage. Please review.

Project coverage is 92.20%. Comparing base (08af12c) to head (0fbaf77).

Files with missing lines	Patch %	Lines
guppylang/checker/stmt_checker.py	85.71%	2 Missing ⚠️

Additional details and impacted files

@@                 Coverage Diff                  @@
##           feat/diagnostics     #621      +/-   ##
====================================================
+ Coverage             92.18%   92.20%   +0.02%     
====================================================
  Files                    65       64       -1     
  Lines                  7201     7060     -141     
====================================================
- Hits                   6638     6510     -128     
+ Misses                  563      550      -13     

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[qartik]

The error messages look way more friendly now! Had a question about one of them. Unsure if it's even part of this PR.

[qartik]

Would it be an easier read if this error was:

Suggested change

	| ^ Attribute `z` not found on type `int`
	| ^ Attribute `z` of type `int` not found

or even better

Suggested change

	| ^ Attribute `z` not found on type `int`
	| ^ `MyStruct` has no attribute `z` of type `int`

I actually don't see the relevance of the inferred type here, the error message on the left is quite descriptive as is. Perhaps I am missing some context here.

[mark-koch]

Oops yes it's supposed to say "MyStruct" instead of "int" 👍