perf: Introduce MemReader to file buffer in Parquet reader

[coastalwhite]

This PR introduces three structures:

• MemReader: Abstraction over part of a Parquet file loaded into memory
• MemReaderSlice: A slice of a MemReader. This should should not be kept around outside the Parquet crate.
• CowBuffer: A Cow that abstracts between a MemReaderSlice and a Vec<u8>.

Following this PR, we can avoid copying the memory around in the Parquet crate. This also allows us to guarantee that the memory is in RAM and does not need to be loaded from disk anymore. Leading to less page faults.

Later it might be useful to make the reads a bit more granular so that we don't need to load unnecessary data pages.

[codecov]

Codecov Report

Attention: Patch coverage is 67.93249% with 76 lines in your changes missing coverage. Please review.

Project coverage is 80.38%. Comparing base (ebba58d) to head (dec9f03).
Report is 10 commits behind head on main.

Files	Patch %	Lines
.../polars-parquet/src/parquet/read/page/memreader.rs	67.30%	34 Missing ⚠️
...rates/polars-parquet/src/arrow/write/dictionary.rs	40.00%	12 Missing ⚠️
...tes/polars-parquet/src/parquet/read/page/reader.rs	71.87%	9 Missing ⚠️
crates/polars-parquet/src/parquet/page/mod.rs	76.19%	5 Missing ⚠️
...arrow/read/deserialize/fixed_size_binary/nested.rs	0.00%	4 Missing ⚠️
...s/polars-parquet/src/arrow/read/deserialize/mod.rs	0.00%	3 Missing ⚠️
...tes/polars-parquet/src/parquet/read/compression.rs	57.14%	3 Missing ⚠️
.../arrow/read/deserialize/fixed_size_binary/basic.rs	33.33%	2 Missing ⚠️
...w/read/deserialize/fixed_size_binary/dictionary.rs	0.00%	1 Missing ⚠️
...quet/src/arrow/read/deserialize/primitive/basic.rs	0.00%	1 Missing ⚠️
... and 2 more

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #17712      +/-   ##
==========================================
- Coverage   80.46%   80.38%   -0.09%     
==========================================
  Files        1498     1501       +3     
  Lines      196457   196723     +266     
  Branches     2790     2793       +3     
==========================================
+ Hits       158075   158131      +56     
- Misses      37869    38079     +210     
  Partials      513      513              

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