qpack: Lazy ring buffer allocation #899

Job	Run time
build (ubuntu-24.04, gcc, autotools)	46s
build-windows (x86)	41s
build (ubuntu-24.04, gcc, cmake)	48s
build-cross (x86_64-w64-mingw32)	1m 34s
build-windows (x64)	1m 18s
build-cross (i686-w64-mingw32)	2m 30s
build (ubuntu-24.04, clang, autotools)	45s
build (ubuntu-24.04, clang, distcheck)	50s
build (ubuntu-24.04, clang, cmake)	47s
build (macos-13, gcc, autotools)	1m 16s
build (macos-13, gcc, cmake)	1m 15s
build (macos-13, clang, autotools)	1m 13s
build (macos-13, clang, cmake)	1m 10s
build (macos-14, gcc, autotools)	39s
build (macos-14, gcc, cmake)	41s
build (macos-14, clang, autotools)	38s
build (macos-14, clang, cmake)	37s
release	0s
	17m 28s

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