[Python] Fix Array.length/.Length to use len() for plain list interop

[dbrattli]

Summary

• Fix Array.length, .Length, Array.isEmpty, and ResizeArray.Count to compile to len() instead of .length property access in Python
• The .length property only exists on FSharpArray (Rust-backed) but breaks on plain Python lists from Emit, unbox, or native APIs like json.loads
• len() works universally since FSharpArray implements __len__, and is wrapped in int32() to preserve the expected return type
• Add regression tests that exercise Array.length, .Length, and Array.isEmpty on plain Python lists via emitPyExpr

[github-actions]

Python Type Checking Results (Pyright)

Metric	Value
Total errors	13
Files with errors	2
Excluded files	2
New errors	✅ No

Excluded files with errors (2 files)

These files have known type errors and are excluded from CI. Remove from pyrightconfig.ci.json as errors are fixed.

File	Errors	Status
temp/tests/Python/test_applicative.py	12	Excluded
temp/tests/Python/fable_modules/thoth_json_python/encode.py	1	Excluded