refactor: Turn linearity checking into separate compiler stage

[mark-koch]

Closes #272

[mark-koch]

For some reason bool.__xor__ is missing (see #274).

The test worked before since the linearity violation triggered an error before we got to this point. Now we type check everything first, so this has to be fixed (similar for the remaining modified tests)

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 97.88732% with 3 lines in your changes missing coverage. Please review.

Project coverage is 91.47%. Comparing base (792fb87) to head (f0dec41).

Files	Patch %	Lines
guppylang/checker/linearity_checker.py	97.50%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #273      +/-   ##
==========================================
+ Coverage   91.39%   91.47%   +0.07%     
==========================================
  Files          44       45       +1     
  Lines        5023     5116      +93     
==========================================
+ Hits         4591     4680      +89     
- Misses        432      436       +4     

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[aborgna-q]

Nice and tidy.

The comments on _check_comprehension are quite useful.

[aborgna-q]

Is this a drive-by?

[mark-koch]

No this is required now that we annotate the LHS of assignments with types

guppylang/guppylang/checker/stmt_checker.py

Lines 49 to 56 in f0dec41

	def _check_assign(self, lhs: ast.expr, ty: Type, node: ast.stmt) -> None:
	"""Helper function to check assignments with patterns."""
	match lhs:
	# Easiest case is if the LHS pattern is a single variable.
	case ast.Name(id=x):
	# Store the type in the AST
	with_type(ty, lhs)
	self.ctx.locals[x] = Variable(x, ty, lhs)

If we don't make a copy, the type checker will see that a type has been assigned when the variable is used the next time and won't bother checking again which leads incorrect behaviour