WIP: Format imports in Rust code

[andygrove]

Changes in this PR:

• Add rustfmt.toml with rules for formatting imports. These require cargo +nightly fmt
• Add CI formatting check that runs cargo +nightly fmt
• Disable formatting in pre-commit hook because it does not support +nightly (see [ENH] Find alternative to pre-commit-rust #810)
• Formatting changes resulting from running cargo +nightly fmt

[codecov-commenter]

Codecov Report

Merging #811 (92ebe77) into main (94f96a0) will decrease coverage by 0.13%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main     #811      +/-   ##
==========================================
- Coverage   74.88%   74.74%   -0.14%     
==========================================
  Files          71       71              
  Lines        3588     3588              
  Branches      748      748              
==========================================
- Hits         2687     2682       -5     
  Misses        771      771              
- Partials      130      135       +5     

Impacted Files	Coverage Δ
dask_sql/physical/rel/custom/export_model.py	88.88% <0.00%> (-2.78%)	⬇️
dask_sql/physical/rel/logical/window.py	95.37% <0.00%> (-1.74%)	⬇️
dask_sql/_version.py	32.27% <0.00%> (-0.29%)	⬇️

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