Align structure names with spec

[alamb]

A proposed update to the ALP implementation

• [Parquet] ALP encoder/decoder support apache/arrow-rs#9372

Rather than aligning with C++ I think it would make the code easer to understand if the names mirrored what is in the spec, namely

• GH-533: Add ALP (Adaptive Lossless floating-Point) encoding specification apache/parquet-format#557

[sdf-jkl]

FYI, parquet crate does fmt via

cargo fmt -p parquet --  --config skip_children=true `find ./parquet -name "*.rs" \! -name format.rs`

[alamb]

FYI, parquet crate does fmt via

cargo fmt -p parquet --  --config skip_children=true `find ./parquet -name "*.rs" \! -name format.rs`

Sorry I keep breaking this -- will fix