gh-90815: Add mimalloc memory allocator #92600

Job	Run time
Check for source changes	14s
Windows (x64)	23m 44s
Windows (arm64)	5m 50s
Windows (x86)	26m 15s
Check if generated files are up to date	6m 46s
Address sanitizer	16m 4s
Ubuntu SSL tests with OpenSSL (1.1.1w)	3m 14s
Hypothesis tests on Ubuntu	6m 52s
Ubuntu SSL tests with OpenSSL (3.0.11)	3m 7s
Ubuntu SSL tests with OpenSSL (3.1.3)	3m 19s
macOS (free-threaded)	0s
Ubuntu (free-threaded)	0s
CIFuzz (address)	23m 30s
CIFuzz (undefined)	25m 25s
CIFuzz (memory)	25m 20s
macOS / build and test	20m 19s
Ubuntu / build and test	13m 23s
Docs / Docs	3m 23s
Docs / Doctest	11m 25s
Docs / Docs (Oldest Sphinx)	2m 31s
All required checks pass	2s
	3h 40m 43s

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