add example with run-time-parametrized matmul #6110

Job	Run time
ubuntu-22.04 llvm assert=ON rtti=ON	5m 17s
ubuntu-22.04 llvm assert=ON rtti=OFF	5m 28s
ubuntu-22.04 llvm assert=OFF rtti=ON	5m 8s
ubuntu-22.04 llvm assert=OFF rtti=OFF	6m 20s
ubuntu-22.04 gcc assert=ON rtti=ON	5m 19s
ubuntu-22.04 gcc assert=ON rtti=OFF	5m 4s
ubuntu-22.04 gcc assert=OFF rtti=ON	5m 11s
ubuntu-22.04 gcc assert=OFF rtti=OFF	4m 50s
ubuntu-24.04 llvm assert=ON rtti=ON	5m 10s
ubuntu-24.04 llvm assert=ON rtti=OFF	5m 23s
ubuntu-24.04 llvm assert=OFF rtti=ON	5m 9s
ubuntu-24.04 llvm assert=OFF rtti=OFF	5m 25s
ubuntu-24.04 gcc assert=ON rtti=ON	5m 44s
ubuntu-24.04 gcc assert=ON rtti=OFF	5m 38s
ubuntu-24.04 gcc assert=OFF rtti=ON	5m 26s
ubuntu-24.04 gcc assert=OFF rtti=OFF	5m 10s
ubuntu-20.04 gcc-11 assert=ON rtti=OFF	5m 11s
ubuntu-20.04 gcc-11 assert=OFF rtti=OFF	5m 36s
ubuntu-20.04 gcc-11 assert=ON rtti=ON	5m 14s
ubuntu-20.04 gcc-11 assert=OFF rtti=ON	5m 24s
windows-2019 msvc assert=ON rtti=ON	9m 24s
windows-2019 msvc assert=ON rtti=OFF	8m 27s
windows-2019 msvc assert=OFF rtti=ON	6m 44s
windows-2019 msvc assert=OFF rtti=OFF	7m 4s
	2h 18m 46s

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