Separate Page IO from Page Decode

[tustvold]

Which issue does this PR close?

Part of #1163

Rationale for this change

This is part of reworking the read path to use less custom abstractions, in particular it splits reading the page bytes from interpreting those bytes.

What changes are included in this PR?

Splits the decode logic out of SerializedPageReader into free functions, and then uses this within ParquetRecordBatchStream to elide a copy.

Are there any user-facing changes?

No

[codecov-commenter]

Codecov Report

Merging #1810 (17412bf) into master (1d31d30) will decrease coverage by 0.04%.
The diff coverage is 61.00%.

❗ Current head 17412bf differs from pull request most recent head dfedade. Consider uploading reports for the commit dfedade to get more accurate results

@@            Coverage Diff             @@
##           master    #1810      +/-   ##
==========================================
- Coverage   83.44%   83.40%   -0.05%     
==========================================
  Files         199      199              
  Lines       56651    56690      +39     
==========================================
+ Hits        47272    47281       +9     
- Misses       9379     9409      +30     

Impacted Files	Coverage Δ
parquet/src/arrow/async_reader.rs	0.00% <0.00%> (ø)
parquet/src/file/serialized_reader.rs	94.95% <88.40%> (+0.49%)	⬆️
arrow/src/datatypes/datatype.rs	65.42% <0.00%> (-0.38%)	⬇️

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[nevi-me]

LGTM