[MAINTENANCE] Adding typehint annotations in backend and data components and fixing mypy errors.

[alexsherstinsky]

Scope

• Adding typehint annotations in backend and data components.
• Fixing a number of mypy errors (many more remain).

Note: this involved removing create_trainer() from LocalTrainingMixin and putting it directly into LocalBackend so as to satisfy the interface requirements of the Backend class.

Code Pull Requests

Please provide the following:

• a clear explanation of what your code does
• if applicable, a reference to an issue
• a reproducible test for your PR (code, config and data sample)

Documentation Pull Requests

Note that the documentation HTML files are in docs/ while the Markdown sources are in mkdocs/docs.

If you are proposing a modification to the documentation you should change only the Markdown files.

api.md is automatically generated from the docstrings in the code, so if you want to change something in that file, first modify ludwig/api.py docstring, then run mkdocs/code_docs_autogen.py, which will create mkdocs/docs/api.md .

[github-actions]

Unit Test Results

  6 files  ±0    6 suites  ±0   20m 59s ⏱️ -24s
12 tests ±0    7 ✔️  -   2    5 💤 +  2  0 ❌ ±0 
60 runs  ±0  30 ✔️  - 12  30 💤 +12  0 ❌ ±0 

Results for commit 7449f64. ± Comparison against base commit 626d9fc.

This pull request skips 2 tests.

tests.regression_tests.benchmark.test_model_performance ‑ test_performance[ames_housing.gbm.yaml]
tests.regression_tests.benchmark.test_model_performance ‑ test_performance[mercedes_benz_greener.gbm.yaml]

♻️ This comment has been updated with latest results.