Refactor reporter loading and imports

[CulmoneY]

Proposed Changes

(Describe your changes here. Also describe the motivation for your changes: what problem do they solve, or how do they improve the application or codebase? If this pull request fixes an open issue, use a keyword to link this pull request to the issue.)

Completed the following two cleanup tasks:

1. Removed unused imports from python_ta/init.py and all files it imports.
2. Wrapped type-only imports in if TYPE_CHECKING guards to avoid unnecessary runtime imports.

...

C Profile Overview:

In Master:

ncalls  tottime  percall  cumtime  percall filename:lineno(function)
      85    0.001    0.000    1.054    0.012 __init__.py:1(<module>)
   712/1    0.005    0.000    0.319    0.319 {built-in method builtins.exec}
   763/1    0.002    0.000    0.319    0.319 <frozen importlib._bootstrap>:1349(_find_and_load)
   761/1    0.001    0.000    0.319    0.319 <frozen importlib._bootstrap>:1304(_find_and_load_unlocked)

In Branch:

ncalls  tottime  percall  cumtime  percall filename:lineno(function)
       68    0.001    0.000    0.781    0.011 __init__.py:1(<module>)
    581/1    0.005    0.000    0.225    0.225 {built-in method builtins.exec}
    615/1    0.001    0.000    0.225    0.225 <frozen importlib._bootstrap>:1349(_find_and_load)
    613/1    0.001    0.000    0.225    0.225 <frozen importlib._bootstrap>:1304(_find_and_load_unlocked)

Difference of 0.273 seconds 🥳

Type of Change

(Write an X or a brief description next to the type or types that best describe your changes.)

Type	Applies?
🚨 Breaking change (fix or feature that would cause existing functionality to change)
✨ New feature (non-breaking change that adds functionality)
🐛 Bug fix (non-breaking change that fixes an issue)
♻️ Refactoring (internal change to codebase, without changing functionality)	x
🚦 Test update (change that only adds or modifies tests)
📚 Documentation update (change that only updates documentation)
📦 Dependency update (change that updates a dependency)
🔧 Internal (change that only affects developers or continuous integration)

Checklist

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Before opening your pull request:

• I have performed a self-review of my changes.
  • Check that all changed files included in this pull request are intentional changes.
  • Check that all changes are relevant to the purpose of this pull request, as described above.
• I have added tests for my changes, if applicable.
  • This is required for all bug fixes and new features.
• I have updated the project documentation, if applicable.
  • This is required for new features.
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After opening your pull request:

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• I have reviewed the test coverage changes reported by Coveralls.
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Questions and Comments

(Include any questions or comments you have regarding your changes.)

[coveralls]

Pull Request Test Coverage Report for Build 15338828631

Details

• 28 of 49 (57.14%) changed or added relevant lines in 14 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.5%) to 92.94%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
python_ta/init.py	2	3	66.67%
python_ta/cfg/cfg_generator.py	2	3	66.67%
python_ta/checkers/forbidden_import_checker.py	2	3	66.67%
python_ta/checkers/global_variables_checker.py	2	3	66.67%
python_ta/checkers/invalid_name_checker.py	2	3	66.67%
python_ta/checkers/possibly_undefined_checker.py	2	3	66.67%
python_ta/checkers/redundant_assignment_checker.py	2	3	66.67%
python_ta/checkers/unnecessary_indexing_checker.py	2	3	66.67%
python_ta/reporters/plain_reporter.py	2	3	66.67%
python_ta/checkers/condition_logic_checker.py	2	4	50.0%

Totals
Change from base Build 15242483438:	-0.5%
Covered Lines:	3436
Relevant Lines:	3697

---

💛 - Coveralls

[david-yz-liu]

@CulmoneY nice work, I just left a few inline comments.

In the PR description it would be great if you could put in a CProfile comparison of the before and after metrics with your changes. This would help put in context how much of an improvement this actually was. (This is a good practice for any PRs that are focused on efficiency.)