docs: update Python style docs to Ruff, remove TVM EP artifacts

[MaanavD]

Description

Fixes documentation discrepancies found by comparing in-repo docs against actual codebase configuration.

Python Code Style docs (docs/Coding_Conventions_and_Standards.md)

• Black → Ruff: The docs recommended Black and isort, but the actual formatter/linter configured in .lintrunner.toml and requirements-lintrunner.txt is Ruff
• Removed stale pydocstyle recommendation (not configured in lintrunner or installed)
• Updated PyCharm section to link to Ruff docs instead of Black docs
• Fixed typo: "development is VS Code" → "development in VS Code"

TVM EP cleanup

The TVM Execution Provider was removed in Nov 2024 (commit 13346fdf18), but a few artifacts remained:

• Removed kTvmExecutionProvider constant from include/onnxruntime/core/graph/constants.h (no code references it)
• Removed commented-out DefaultTvmExecutionProvider() declaration from default_providers.h
• Removed dead test_tvm_imported test method from onnxruntime_test_python.py

Note: The available_providers_without_tvm variable in onnxruntime_test_python.py is used in ~15 places. Since TVM EP is removed, the filter is a harmless no-op. Cleaning that up is a larger refactor best done separately.

Motivation and Context

Audited all major in-repo documentation against the actual codebase. The C API Guidelines, OperatorKernels.md, ContribOperators.md, Versioning.md, and PR Guidelines were all verified as accurate. Only the Python style section and TVM EP remnants were out of date.