perf: reduce memory usage for index

[aawsome]

This PR restricts the supported pack count to 2^32. By doing so it allows to store the pack file index as u32 instead of usize reducing the index size per blob from 52 to 48 bytes, i.e. about 7.5% reduction in memory usage (for command which use a full index),

[codecov]

Codecov Report

❌ Patch coverage is 83.33333% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 52.6%. Comparing base (e8b6425) to head (c3de569).

Files with missing lines	Patch %	Lines
crates/core/src/index/binarysorted.rs	83.3%	1 Missing ⚠️

Additional details and impacted files

Files with missing lines	Coverage Δ
crates/core/src/index/binarysorted.rs	82.3% <83.3%> (-2.1%)	⬇️

... and 20 files with indirect coverage changes

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