[Geneva] Optimize metrics exporter serializer

[pentp]

Higher-level changes include serializing resource level tags only once for OtlpProtobufMetricExporter.
Most of the changes are just low-level optimizations for efficient buffer access, single-pass string encoding, etc.

BenchmarkDotNet v0.14.0, Windows 10 (10.0.19045.5247/22H2/2022Update)
Intel Core i7-7700K CPU 4.20GHz (Kaby Lake), 1 CPU, 8 logical and 4 physical cores
.NET SDK 9.0.200-preview.0.24575.35
  [Host]     : .NET 9.0.0 (9.0.24.52809), X64 RyuJIT AVX2
  DefaultJob : .NET 9.0.0 (9.0.24.52809), X64 RyuJIT AVX2

BASELINE	Mean	Error	StdDev	Allocated
SerializeCounterMetricItemWith3Dimensions	162.62 ns	1.355 ns	1.267 ns	-
SerializeCounterMetricItemWith4Dimensions	179.49 ns	1.450 ns	1.356 ns	-
ExportCounterMetricItemWith3Dimensions	181.36 ns	1.158 ns	1.083 ns	-
ExportCounterMetricItemWith4Dimensions	199.94 ns	0.673 ns	0.597 ns	-
SerializeHistogramMetricItemWith3Dimensions	275.98 ns	2.971 ns	2.634 ns	-
SerializeHistogramMetricItemWith4Dimensions	296.83 ns	3.165 ns	2.961 ns	-
ExportHistogramMetricItemWith3Dimensions	299.81 ns	2.303 ns	1.798 ns	-
ExportHistogramMetricItemWith4Dimensions	334.96 ns	6.634 ns	6.813 ns	-
SerializeCounterMetricItemWith3Dimensions_Otlp	375.91 ns	2.072 ns	1.730 ns	48 B
SerializeCounterMetricItemWith4Dimensions_Otlp	433.05 ns	2.902 ns	2.715 ns	48 B
ExportCounterMetricItemWith3Dimensions_Otlp	378.03 ns	2.738 ns	2.427 ns	48 B
ExportCounterMetricItemWith4Dimensions_Otlp	436.66 ns	2.883 ns	2.697 ns	48 B
SerializeHistogramMetricItemWith3Dimensions_Otlp	468.75 ns	2.976 ns	2.784 ns	48 B
SerializeHistogramMetricItemWith4Dimensions_Otlp	519.62 ns	3.066 ns	2.560 ns	48 B
ExportHistogramMetricItemWith3Dimensions_Otlp	470.72 ns	4.137 ns	3.668 ns	48 B
ExportHistogramMetricItemWith4Dimensions_Otlp	531.59 ns	3.729 ns	3.305 ns	48 B

PR	Mean	Error	StdDev	Allocated
SerializeCounterMetricItemWith3Dimensions	134.24 ns	0.803 ns	0.671 ns	-
SerializeCounterMetricItemWith4Dimensions	152.22 ns	0.909 ns	0.850 ns	-
ExportCounterMetricItemWith3Dimensions	131.44 ns	1.095 ns	0.971 ns	-
ExportCounterMetricItemWith4Dimensions	147.23 ns	1.459 ns	1.365 ns	-
SerializeHistogramMetricItemWith3Dimensions	191.51 ns	1.098 ns	0.973 ns	-
SerializeHistogramMetricItemWith4Dimensions	211.51 ns	1.603 ns	1.421 ns	-
ExportHistogramMetricItemWith3Dimensions	190.01 ns	1.047 ns	0.928 ns	-
ExportHistogramMetricItemWith4Dimensions	204.39 ns	1.226 ns	1.147 ns	-
SerializeCounterMetricItemWith3Dimensions_Otlp	145.69 ns	1.172 ns	1.096 ns	-
SerializeCounterMetricItemWith4Dimensions_Otlp	161.80 ns	1.177 ns	1.101 ns	-
ExportCounterMetricItemWith3Dimensions_Otlp	146.14 ns	0.812 ns	0.678 ns	-
ExportCounterMetricItemWith4Dimensions_Otlp	191.51 ns	0.835 ns	0.697 ns	-
SerializeHistogramMetricItemWith3Dimensions_Otlp	188.66 ns	1.410 ns	1.319 ns	-
SerializeHistogramMetricItemWith4Dimensions_Otlp	204.14 ns	0.871 ns	0.727 ns	-
ExportHistogramMetricItemWith3Dimensions_Otlp	185.20 ns	0.781 ns	0.692 ns	-
ExportHistogramMetricItemWith4Dimensions_Otlp	208.30 ns	1.162 ns	1.030 ns	-

[github-actions]

This PR was marked stale due to lack of activity. It will be closed in 7 days.