cbits: integrate mimalloc as a default memory allocator #11635

Job	Run time
build (ubuntu-latest)	4m 7s
build (macos-14)	3m 38s
Build jj-lib without Git support	42s
build (windows-latest)	8m 42s
cargo-deny (advisories)	25s
build (ubuntu-latest, --all-features)	5m 4s
cargo-deny (bans licenses sources)	23s
Check protos	26s
Clippy check	2m 30s
Check that MkDocs can build the docs with Poetry 1.8	24s
Check that MkDocs can build the docs	25s
Check formatting	18s
	27m 4s

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