feat!: Add qualified imports and make them the default

[mark-koch]

Closes #426.

BREAKING CHANGE: GuppyModule.load no longer loads the content of modules but instead just brings the name of the module into scope. Use GuppyModule.load_all to get the old behaviour.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 84.61538% with 16 lines in your changes missing coverage. Please review.

Project coverage is 92.55%. Comparing base (e23b666) to head (642cf45).

Files with missing lines	Patch %	Lines
guppylang/module.py	78.57%	6 Missing :warning:
guppylang/tys/parsing.py	85.71%	6 Missing :warning:
guppylang/checker/expr_checker.py	87.50%	3 Missing :warning:
guppylang/decorator.py	0.00%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #443 +/- ## ========================================== + Coverage 92.53% 92.55% +0.01% ========================================== Files 48 49 +1 Lines 5249 5303 +54 ========================================== + Hits 4857 4908 +51 - Misses 392 395 +3 ```

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