Push qqbar_get_str_nd to qqbar.h #1611

Job	Run time
Alpine Linux, musl, 32-bit (assert, x1.5)	14m 10s
macOS-M1, Clang (x3)	12m 27s
macOS-x86 Clang with BLAS (x2)	15m 53s
GCC sanity check	1m 59s
MinGW GCC (x0.5)	10m 30s
MSVC (x1)	8m 53s
Nemo.jl (temporary branch)	16m 23s
Ubuntu Clang with examples (x5)	13m 14s
Ubuntu GCC, Code Coverage (x10)	25m 23s
Ubuntu GCC with NTL (assert, x2)	8m 42s
	2h 7m 34s

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