decrease disk cache overhead

[arvidn]

only keep a pointer rather than a whole disk_buffer_holder in the cached_block_entry in the cache, decreasing the overhead of the cache.

[Copilot]

Pull request overview

This PR reduces disk cache per-block memory overhead by replacing stored disk_buffer_holder ownership in cache entries with a pointer-only reference, and plumbing piece sizing to support correct block-span sizing during hashing.

Changes:

• Introduces disk_buffer_ref and updates cache block entries to store pointer-only buffer ownership.
• Updates disk_cache to compute correct per-block span sizes (including shorter last blocks) via a new piece_size parameter.
• Adjusts disk I/O and unit tests to provide the new piece sizing metadata to the cache.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
include/libtorrent/disk_buffer_holder.hpp	Adds disk_buffer_ref; changes bulk_free_buffer ctor/add API.
src/disk_buffer_holder.cpp	Implements disk_buffer_ref moves and new bulk_free_buffer::add.
include/libtorrent/aux_/disk_cache.hpp	Switches cached_block_entry to disk_buffer_ref; updates buffer access API and piece params; adds cache allocator member.
src/disk_cache.cpp	Implements new buffer accessors and updates hashing/flush/free paths to use pointer-only buffer refs and batched frees.
src/pread_disk_io.cpp	Supplies new piece_size field when inserting cache blocks.
test/test_disk_cache.cpp	Updates test fixture piece params to include piece_size.
include/libtorrent/fwd.hpp	Forward-declares disk_buffer_ref.

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[Copilot]

Pull request overview

Copilot reviewed 7 out of 7 changed files in this pull request and generated 4 comments.

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[Copilot]

Pull request overview

Copilot reviewed 9 out of 9 changed files in this pull request and generated 1 comment.

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[Copilot]

Pull request overview

Copilot reviewed 12 out of 12 changed files in this pull request and generated no new comments.

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[Copilot]

Pull request overview

Copilot reviewed 12 out of 12 changed files in this pull request and generated 1 comment.

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[Copilot]

Pull request overview

Copilot reviewed 13 out of 13 changed files in this pull request and generated 1 comment.

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