Obtain filepath from Dask DataFrame

[sarahyurick]

Builds upon #1074

Uses part of https://github.com/jdye64/dask-sql/blob/expand_predicate_pushdown/dask_sql/physical/rel/logical/table_scan.py#L112-134

For some reason, this doesn't work with #1102 yet, indicating some error on the DPP side(?), even though DPP is able to obtain the correct filepaths by using this PR. So DPP still just returns the original plan when create_table uses a Dask DataFrame instead of a Parquet filepath.

[codecov-commenter]

Codecov Report

Merging #1145 (b35ea00) into main (41cb27a) will increase coverage by 0.14%.
The diff coverage is 100.00%.

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@@            Coverage Diff             @@
##             main    #1145      +/-   ##
==========================================
+ Coverage   81.43%   81.58%   +0.14%     
==========================================
  Files          78       78              
  Lines        4395     4403       +8     
  Branches      797      798       +1     
==========================================
+ Hits         3579     3592      +13     
+ Misses        640      631       -9     
- Partials      176      180       +4     

Impacted Files	Coverage Δ
dask_sql/context.py	93.96% <100.00%> (+0.18%)	⬆️

... and 1 file with indirect coverage changes

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[jdye64]

Logic looks good. Had one recommendation around a utility function to use if it fits your needs. If it doesn't don't worry about it though.

[ayushdg]

Does the parquet_ddf fixture work for the test here, or does it explicitly need to be redefined here?