Reduce string allocations where possible

[jtescher]

Reduce string allocations where static strs can be used and only clone resources if they are set.

performance improvements

start-end-span/always-sample
                        time:   [420.87 ns 424.12 ns 427.52 ns]
                        change: [-28.404% -27.348% -26.230%] (p = 0.00 < 0.05)
                        Performance has improved.
Found 4 outliers among 100 measurements (4.00%)
  1 (1.00%) high mild
  3 (3.00%) high severe
start-end-span/never-sample
                        time:   [150.86 ns 151.45 ns 152.08 ns]
                        change: [-35.664% -33.873% -32.391%] (p = 0.00 < 0.05)
                        Performance has improved.
Found 6 outliers among 100 measurements (6.00%)
  5 (5.00%) high mild
  1 (1.00%) high severe

start-end-span-4-attrs/always-sample
                        time:   [1.9644 us 1.9784 us 1.9936 us]
                        change: [-17.564% -16.436% -15.363%] (p = 0.00 < 0.05)
                        Performance has improved.
Found 3 outliers among 100 measurements (3.00%)
  2 (2.00%) high mild
  1 (1.00%) high severe
start-end-span-4-attrs/never-sample
                        time:   [190.61 ns 191.81 ns 193.05 ns]
                        change: [-27.437% -26.276% -24.883%] (p = 0.00 < 0.05)
                        Performance has improved.
Found 13 outliers among 100 measurements (13.00%)
  6 (6.00%) high mild
  7 (7.00%) high severe

start-end-span-8-attrs/always-sample
                        time:   [3.4251 us 3.4545 us 3.4851 us]
                        change: [-12.269% -10.913% -9.5738%] (p = 0.00 < 0.05)
                        Performance has improved.
Found 2 outliers among 100 measurements (2.00%)
  1 (1.00%) low mild
  1 (1.00%) high mild
start-end-span-8-attrs/never-sample
                        time:   [228.22 ns 229.16 ns 230.13 ns]
                        change: [-25.206% -24.434% -23.704%] (p = 0.00 < 0.05)
                        Performance has improved.
Found 4 outliers among 100 measurements (4.00%)
  4 (4.00%) high mild

start-end-span-all-attr-types/always-sample
                        time:   [2.6734 us 2.6973 us 2.7247 us]
                        change: [-12.791% -11.390% -10.077%] (p = 0.00 < 0.05)
                        Performance has improved.
Found 8 outliers among 100 measurements (8.00%)
  2 (2.00%) low mild
  4 (4.00%) high mild
  2 (2.00%) high severe
start-end-span-all-attr-types/never-sample
                        time:   [202.75 ns 203.76 ns 204.82 ns]
                        change: [-27.168% -26.470% -25.712%] (p = 0.00 < 0.05)
                        Performance has improved.
Found 7 outliers among 100 measurements (7.00%)
  1 (1.00%) low mild
  4 (4.00%) high mild
  2 (2.00%) high severe

start-end-span-all-attr-types-2x/always-sample
                        time:   [3.9943 us 4.0204 us 4.0470 us]
                        change: [-11.299% -9.8533% -8.5633%] (p = 0.00 < 0.05)
                        Performance has improved.
Found 4 outliers among 100 measurements (4.00%)
  3 (3.00%) high mild
  1 (1.00%) high severe
start-end-span-all-attr-types-2x/never-sample
                        time:   [266.36 ns 269.42 ns 272.70 ns]
                        change: [-18.999% -17.821% -16.498%] (p = 0.00 < 0.05)
                        Performance has improved.
Found 7 outliers among 100 measurements (7.00%)
  3 (3.00%) high mild
  4 (4.00%) high severe

[frigus02]

Nice. I think this even makes APIs like Tracer::start a bit nicer to use because you can pass in both &str and String directly.

[TommyCpp]

Nice improvement 👍