Faster stringify cookie with benchmarks

[blakeembrey]

I decided to try investigating if anything in #250 holds true, and found the opposite for string concatenation. Updated to use string concatenation to improve performance.

Before:

 ✓ src/stringify-cookie.bench.ts > cookie.stringifyCookie 7195ms
     name                         hz     min     max    mean     p75     p99    p995    p999     rme  samples
   · empty             19,138,902.74  0.0000  0.0572  0.0001  0.0000  0.0001  0.0001  0.0002  ±0.11%  9569452
   · simple             5,777,350.07  0.0001  0.3515  0.0002  0.0002  0.0002  0.0003  0.0006  ±0.39%  2888676
   · undefined values   3,129,664.63  0.0002  0.3241  0.0003  0.0003  0.0004  0.0004  0.0008  ±0.46%  1564833
   · 10 cookies           765,737.48  0.0012  0.4257  0.0013  0.0013  0.0014  0.0016  0.0020  ±0.34%   382869
   · 100 cookies           78,240.71  0.0122  0.4788  0.0128  0.0128  0.0137  0.0160  0.0424  ±0.39%    39121

After:

 ✓ src/stringify-cookie.bench.ts > cookie.stringifyCookie 7958ms
     name                         hz     min     max    mean     p75     p99    p995    p999     rme   samples
   · empty             21,654,747.61  0.0000  0.1649  0.0000  0.0000  0.0001  0.0001  0.0002  ±0.14%  10827374
   · simple             7,345,985.72  0.0000  0.0540  0.0001  0.0001  0.0002  0.0002  0.0003  ±0.10%   3672994
   · undefined values   3,820,139.53  0.0002  0.0491  0.0003  0.0003  0.0003  0.0004  0.0004  ±0.11%   1910070
   · 10 cookies           854,240.43  0.0010  0.4322  0.0012  0.0012  0.0013  0.0014  0.0019  ±0.44%    427121
   · 100 cookies           85,417.71  0.0110  0.4168  0.0117  0.0117  0.0126  0.0160  0.0470  ±0.44%     42709

[sheplu]

Just a change for the folder that should host the two new bench files
Other than than LGTM!

[sheplu]

LGTM