🧑‍💻 ToString: improve test and bench setup

[ReneWerner87]

• add string slice case
• add parallel instruction for child tests
• benchmark table and parallel execution

[ReneWerner87]

before:

after:

[ReneWerner87]

before:

Benchmark_ToString/[]string-12         	27281485	        37.12 ns/op	      48 B/op	       3 allocs/op
Benchmark_ToString/[]string-12         	28435568	        39.74 ns/op	      48 B/op	       3 allocs/op
Benchmark_ToString/[]int-12            	36790112	        33.60 ns/op	      24 B/op	       3 allocs/op
Benchmark_ToString/[]int-12            	32494309	        34.20 ns/op	      24 B/op	       3 allocs/op
Benchmark_ToString/[]interface_{}-12   	 8995060	       116.0 ns/op	      96 B/op	       5 allocs/op
Benchmark_ToString/[]interface_{}-12   	 9844160	       114.4 ns/op	      96 B/op	       5 allocs/op

after (more allocs but faster):
string builder

Benchmark_ToString/[]string-12         	45700502	        27.50 ns/op	      56 B/op	       4 allocs/op
Benchmark_ToString/[]string-12         	38168848	        29.37 ns/op	      56 B/op	       4 allocs/op
Benchmark_ToString/[]int-12            	94002447	        13.11 ns/op	      24 B/op	       3 allocs/op
Benchmark_ToString/[]int-12            	94167500	        13.67 ns/op	      24 B/op	       3 allocs/op
Benchmark_ToString/[]interface_{}-12   	11595938	       103.8 ns/op	     200 B/op	      11 allocs/op
Benchmark_ToString/[]interface_{}-12   	11507626	        99.74 ns/op	     200 B/op	      11 allocs/op

also tested with bytebufferpool

Benchmark_ToString/[]string-12         	14074546	        86.84 ns/op	      48 B/op	       3 allocs/op
Benchmark_ToString/[]string-12         	12282381	        85.03 ns/op	      48 B/op	       3 allocs/op
Benchmark_ToString/[]int-12            	15034382	        81.10 ns/op	      24 B/op	       3 allocs/op
Benchmark_ToString/[]int-12            	15246968	        81.95 ns/op	      24 B/op	       3 allocs/op
Benchmark_ToString/[]interface_{}-12   	 4522510	       273.1 ns/op	     120 B/op	       7 allocs/op
Benchmark_ToString/[]interface_{}-12   	 4322280	       274.7 ns/op	     120 B/op	       7 allocs/op

[gaby]

LGTM so far

[gaby]

LGTM