lore-storage: Make read_into respect the byte range for single-fragment reads

[itsfuad]

What:
Make read_into respect the byte range for single-fragment reads in lore-storage.

Why:
read_into accepts an optional byte range, but both single-fragment branches (compressed and uncompressed) were comparing slice.len() against the full fragment payload instead of the requested range. Any partial read on a file ≤ 256 KiB (the FRAGMENT_SIZE_THRESHOLD) would fail with unexpected size: slice 40 vs buffer 100. The fragmented branch and the sibling read() both handle this correctly, only read_into's single-fragment paths were missing it.

Fixes #25

How:
Added one line to each single-fragment branch to slice the buffer to the requested range before the existing size check and copy:

// compressed
let decompressed = decompressed.freeze().slice(range);

// uncompressed
let buffer = buffer.slice(range);

Testing:
Added a regression test that stores a 100-byte fragment and reads bytes 10..50 into a 40-byte buffer, reproducing the original failure.

[rajpratham1]

This is a focused bug fix that addresses a clear inconsistency in read_into. The change is minimal, aligns the single-fragment paths with the existing fragmented implementation and read(), and includes a regression test that reproduces the original issue. I don't see any blocking concerns.

[mjansson]

Looks good - make sure you follow the guidelines at https://github.com/EpicGames/lore/blob/main/CONTRIBUTING.md#dco-sign-off and do the DCO signoff on the commits to let us take this in.

[itsfuad]

Looks good - make sure you follow the guidelines at https://github.com/EpicGames/lore/blob/main/CONTRIBUTING.md#dco-sign-off and do the DCO signoff on the commits to let us take this in.

@mjansson Done. Review please.

[itsfuad]

@mjansson Fixed clippy issues in workflow run.