refactor(perf): improve tag serialization

[mdobosz-isp]

Benchmark changes:

benchmark                                       old ns/op     new ns/op     delta
Benchmark_0Tags_100Emits-4                      30814         28782         -6.59%
BenchmarkTags_5Tags_100Emits-4                  42317         53051         +25.37%
BenchmarkTags_5Tags_100Emits_WithInline-4       143681        107949        -24.87%
BenchmarkTags_10Tags_1000Emits-4                989118        526336        -46.79%
BenchmarkTags_10Tags_1000Emits_WithInline-4     2449188       1372939       -43.94%
BenchmarkTags_15Tags_100Emits-4                 77491         69507         -10.30%
BenchmarkTags_15Tags_100Emits_WithInline-4      190324        156984        -17.52%

benchmark                                       old allocs     new allocs     delta
Benchmark_0Tags_100Emits-4                      1              1              +0.00%
BenchmarkTags_5Tags_100Emits-4                  17             7              -58.82%
BenchmarkTags_5Tags_100Emits_WithInline-4       717            507            -29.29%
BenchmarkTags_10Tags_1000Emits-4                32             12             -62.50%
BenchmarkTags_10Tags_1000Emits_WithInline-4     7032           5012           -28.73%
BenchmarkTags_15Tags_100Emits-4                 47             17             -63.83%
BenchmarkTags_15Tags_100Emits_WithInline-4      747            517            -30.79%

benchmark                                       old bytes     new bytes     delta
Benchmark_0Tags_100Emits-4                      48            48            +0.00%
BenchmarkTags_5Tags_100Emits-4                  370           211           -42.97%
BenchmarkTags_5Tags_100Emits_WithInline-4       51900         48528         -6.50%
BenchmarkTags_10Tags_1000Emits-4                751           401           -46.60%
BenchmarkTags_10Tags_1000Emits_WithInline-4     595994        563601        -5.44%
BenchmarkTags_15Tags_100Emits-4                 1012          534           -47.23%
BenchmarkTags_15Tags_100Emits_WithInline-4      68543         64851         -5.39%

[codecov-commenter]

Codecov Report

Merging #16 into master will increase coverage by 0.09%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master      #16      +/-   ##
==========================================
+ Coverage   93.89%   93.99%   +0.09%     
==========================================
  Files           6        6              
  Lines         426      433       +7     
==========================================
+ Hits          400      407       +7     
  Misses         18       18              
  Partials        8        8              

Impacted Files	Coverage Δ
metrics/util.go	91.66% <100.00%> (+1.42%)	⬆️

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