ARROW-11313: [Rust] Fixed size_hint

[jorgecarleitao]

size_hint should return the remaining items, not the total number of items.

[github-actions]

https://issues.apache.org/jira/browse/ARROW-11313

[codecov-io]

Codecov Report

Merging #9258 (f76ceab) into master (1393188) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@ Coverage Diff @@## master #9258 +/- ##
=======================================
Coverage 81.61% 81.61% =======================================
Files 215 215 Lines 51867 51891 +24 =======================================
+ Hits 42329 42353 +24 
Misses 9538 9538 

Impacted Files	Coverage Δ
rust/arrow/src/array/iterator.rs	93.45% <100.00%> (ø)
rust/parquet/src/arrow/schema.rs	91.66% <100.00%> (+0.16%)	⬆️
rust/arrow/src/array/transform/fixed_binary.rs	84.21% <0.00%> (+5.26%)	⬆️

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[alamb]

This looks consistent with https://doc.rust-lang.org/std/iter/trait.Iterator.html#method.size_hint to me. 👍 @jorgecarleitao

I also found another implementation of size_hint but that seems to be doing the right thing: https://github.com/alamb/arrow/blob/master/rust/arrow/src/util/bit_chunk_iterator.rs#L156

[alamb]

I merged this branch locally and ran the tests and everything looked good 👍