feat: add binary string operations (length and concatenation)

[f4t4nt]

Added two new binary string operations to Daft:\n\n- binary.length(): Get length of binary strings in bytes\n- binary.concat(): Concatenate two binary strings\n\nImplemented in Rust with full test coverage including ASCII, UTF-8, and special binary sequences.

[codspeed-hq]

CodSpeed Performance Report

Merging #3646 will improve performances by 34.3%

_{Comparing nishant-binary-string (c887532) with main (6157ad8)}

Summary

⚡ 1 improvements
✅ 26 untouched benchmarks

Benchmarks breakdown

	Benchmark	main	nishant-binary-string	Change
⚡	test_iter_rows_first_row[100 Small Files]	192.6 ms	143.4 ms	+34.3%

[kevinzwang]

Looks great so far!

[codecov]

Codecov Report

Attention: Patch coverage is 84.63303% with 67 lines in your changes missing coverage. Please review.

Project coverage is 76.87%. Comparing base (39bb62c) to head (c887532).
Report is 22 commits behind head on main.

Files with missing lines	Patch %	Lines
src/daft-core/src/series/ops/binary.rs	33.33%	26 Missing ⚠️
src/daft-core/src/array/ops/binary.rs	94.91%	12 Missing ⚠️
src/daft-functions/src/binary/concat.rs	84.21%	12 Missing ⚠️
src/daft-functions/src/binary/slice.rs	71.05%	11 Missing ⚠️
src/daft-functions/src/binary/length.rs	80.64%	6 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3646      +/-   ##
==========================================
- Coverage   77.99%   76.87%   -1.13%     
==========================================
  Files         720      733      +13     
  Lines       88794    93056    +4262     
==========================================
+ Hits        69252    71533    +2281     
- Misses      19542    21523    +1981     

Files with missing lines	Coverage Δ
daft/expressions/expressions.py	93.62% <100.00%> (+0.10%)	⬆️
src/daft-core/src/series/ops/mod.rs	100.00% <ø> (ø)
src/daft-functions/src/lib.rs	0.00% <ø> (ø)
src/daft-functions/src/python/mod.rs	100.00% <100.00%> (ø)
src/daft-functions/src/binary/length.rs	80.64% <80.64%> (ø)
src/daft-functions/src/binary/slice.rs	71.05% <71.05%> (ø)
src/daft-core/src/array/ops/binary.rs	94.91% <94.91%> (ø)
src/daft-functions/src/binary/concat.rs	84.21% <84.21%> (ø)
src/daft-core/src/series/ops/binary.rs	33.33% <33.33%> (ø)

... and 300 files with indirect coverage changes

[kevinzwang]

Looks good so far! In addition to the other comments there's two things you should also do:

• add these functions to our docs by adding a section in docs/source/api_docs/expressions.rst
• implement this for the FixedSizeBinaryArray type as well

[kevinzwang]

Looks good so far! I had some comments on things to clean up.