check template arguments with constexpr

[anonrig]

It seems we forgot to check them using constexpr

Before

BasicBench_AdaURL_url                202523 ns       201802 ns         3461 GHz=4.79069 cycle/byte=44.3605 cycles/url=1.07173k instructions/byte=111.316 instructions/cycle=2.50935 instructions/ns=12.0215 instructions/url=2.68935k ns/url=223.711 speed=102.001M/s time/byte=9.80384ns time/url=236.857ns url/s=4.22195M/s
BasicBench_AdaURL_url_aggregator     166170 ns       166133 ns         4221 GHz=4.79185 cycle/byte=36.7923 cycles/url=888.888 instructions/byte=113.701 instructions/cycle=3.09034 instructions/ns=14.8085 instructions/url=2.74697k ns/url=185.5 speed=123.901M/s time/byte=8.07096ns time/url=194.991ns url/s=5.12843M/s

After

BasicBench_AdaURL_url                194068 ns       194060 ns         3588 GHz=4.79139 cycle/byte=44.2933 cycles/url=1.07011k instructions/byte=111.334 instructions/cycle=2.51357 instructions/ns=12.0435 instructions/url=2.6898k ns/url=223.34 speed=106.07M/s time/byte=9.42769ns time/url=227.77ns url/s=4.3904M/s
BasicBench_AdaURL_url_aggregator     160928 ns       160918 ns         4346 GHz=4.79164 cycle/byte=36.0423 cycles/url=870.768 instructions/byte=113.71 instructions/cycle=3.15491 instructions/ns=15.1172 instructions/url=2.7472k ns/url=181.727 speed=127.916M/s time/byte=7.81761ns time/url=188.871ns url/s=5.29463M/s