feat(silo): use mimalloc as the default allocator

[taepper]

I decided to split up #1045 for the allocator change and the mimalloc option tweaking

[github-actions]

This is a preview of the changelog of the next release. If this branch is not up-to-date with the current main branch, the changelog may not be accurate. Rebase your branch on the main branch to get the most accurate changelog.

Note that this might contain changes that are on main, but not yet released.

Changelog:

0.9.2 (2025-12-02)

Features

• benchmarking: add DEBUG custom variable for running debug builds (541afc8)
• benchmarking: update api-query, enable CSV log file w/ checksum comparisons (3d135d0)
• build: tag images with branch name again (670817c)
• documentation: add documentation for sequence storage format (47e4081)
• silo: add efficient way of computing vertical coverage bitmaps and use them to adapt reference positions (8e7e9f4)
• silo: add reordering of predicates to apply most selective predicates first (1db8cf0)
• silo: better compression for sequences (9eb69c7)
• silo: change IsInCoveredRegion to predicate instead of being its own filter-operator (6fef558)
• silo: enable rewrite of SymbolInSet expressions under Or (5489117)
• silo: split compile function into separate rewrite step (27b7e7c)
• silo: use mimalloc as the default allocator (ee57f33)

Bug Fixes

• build: correctly fix the cppstd for installing the arrow dependency (0c4aed3)
• build: fix Makefile to not repeatedly invoke conan install (346e6a9)
• silo: do not add empty coverage bitmaps (5bd32c7)

[pflanze]

Looks good to me iff this commit actually works, see my comment about allocator.h not being included.