Optimize read buffer compaction and reduce copying #916

Job	Run time
Build with make	3m 10s
Build for 32-bit	33s
Installation tests	27s
RDMA support enabled	24s
Run static checkers	26s
macOS	1m 1s
Windows (MinGW64)	1m 9s
Windows (Cygwin)	2m 42s
CMake 3.7.0 (min. required)	17s
Windows	1m 32s
Build with CMake [gcc-9, cmake-3.13, Release]	2m 52s
Build with CMake [gcc-15, cmake-4.2, Release]	4m 25s
Build with CMake and leak-sanitizer [gcc-15, cmake-4.2, RelWithDebInfo]	4m 4s
Build with CMake and address-sanitizer [gcc-15, cmake-4.2, RelWithDebInfo]	4m 20s
Build with CMake and undefined-sanitizer [gcc-15, cmake-4.2, RelWithDebInfo]	4m 12s
Build with CMake and thread-sanitizer [clang-22, cmake-4.2, RelWithDebInfo]	3m 3s
Build with CMake [clang-22, cmake-4.2, Release]	3m 5s
Build with CMake and thread-sanitizer [gcc-15, cmake-4.2, RelWithDebInfo]	5m 10s
Build with CMake and address-sanitizer [clang-22, cmake-4.2, RelWithDebInfo]	3m 9s
Build with CMake [clang-14, cmake-3.13, Release]	2m 51s
Build with CMake and undefined-sanitizer [clang-22, cmake-4.2, RelWithDebInfo]	3m 6s
Build with CMake and leak-sanitizer [clang-22, cmake-4.2, RelWithDebInfo]	3m 13s
	55m 11s

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