mulmod_shoup and nmod_vec_scalar_mul_nmod #2787

Job	Run time
Alpine Linux, musl, 32-bit (assert, x1.5)	14m 0s
GCC build regression check (no tests)	1m 5s
macOS-x86 Clang with BLAS (x2)	20m 1s
macOS-M1, Clang (x3)	9m 33s
MinGW GCC (x0.5)	10m 27s
MSVC (x1)	8m 35s
Nemo.jl (temporary branch)	11m 50s
Ubuntu Clang with examples (x5)	12m 40s
Ubuntu GCC, Code Coverage (x10)	20m 54s
Ubuntu GCC with NTL (assert, x2)	8m 23s
	1h 57m 28s

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