[CHORE] Add stubs and improve comments for pyo3-exposed abstractions, + driveby type/bug fixes.

[clarkzinzow]

This PR adds .pyi stub definitions for all of our pyo3-exposed classes and functions, adds/improves comments for those abstractions, and makes a bunch of driveby type/bug fixes.

The stub definitions enable stronger mypy type-checking and enable code completion for pyo3 abstractions in IDEs.

[codecov]

Codecov Report

Merging #1377 (71fa0c8) into main (fc10d6d) will increase coverage by 0.54%.
Report is 3 commits behind head on main.
The diff coverage is 100.00%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1377      +/-   ##
==========================================
+ Coverage   87.25%   87.80%   +0.54%     
==========================================
  Files          61       60       -1     
  Lines        6059     6025      -34     
==========================================
+ Hits         5287     5290       +3     
+ Misses        772      735      -37     

Files Changed	Coverage Δ
daft/__init__.py	26.47% <ø> (+0.15%)	⬆️
daft/logical/schema.py	93.00% <ø> (ø)
daft/runners/runner_io.py	86.66% <ø> (ø)
daft/table/table.py	82.01% <ø> (ø)
daft/context.py	70.52% <100.00%> (+0.63%)	⬆️
daft/io/common.py	90.90% <100.00%> (ø)
daft/logging.py	92.30% <100.00%> (ø)
daft/runners/ray_runner.py	91.20% <100.00%> (+0.02%)	⬆️
daft/udf.py	94.44% <100.00%> (ø)

... and 1 file with indirect coverage changes