Add benchmark for synchronous gauge measurement

[dashpole]

These were missing from our benchmarks for synchronous instruments.

Single-threaded:

goos: linux
goarch: amd64
pkg: go.opentelemetry.io/otel/sdk/metric
cpu: Intel(R) Xeon(R) CPU @ 2.20GHz
BenchmarkSyncMeasure/NoView/Float64Gauge/Attributes/0         	  114369	       106.0 ns/op	       0 B/op	       0 allocs/op
BenchmarkSyncMeasure/NoView/Float64Gauge/Attributes/1         	  106424	       119.4 ns/op	       0 B/op	       0 allocs/op
BenchmarkSyncMeasure/NoView/Float64Gauge/Attributes/10        	   79513	       128.7 ns/op	       0 B/op	       0 allocs/op
BenchmarkSyncMeasure/NoView/Int64Gauge/Attributes/0         	  110667	       166.0 ns/op	       0 B/op	       0 allocs/op
BenchmarkSyncMeasure/NoView/Int64Gauge/Attributes/1         	  103809	       150.2 ns/op	       0 B/op	       0 allocs/op
BenchmarkSyncMeasure/NoView/Int64Gauge/Attributes/10        	   76430	       144.2 ns/op	       0 B/op	       0 allocs/op

Parallel:

goos: linux
goarch: amd64
pkg: go.opentelemetry.io/otel/sdk/metric
cpu: Intel(R) Xeon(R) CPU @ 2.20GHz
BenchmarkSyncMeasure/NoView/Float64Gauge/Attributes/0-24         	   40507	       283.4 ns/op	       0 B/op	       0 allocs/op
BenchmarkSyncMeasure/NoView/Float64Gauge/Attributes/1-24         	   43918	       305.3 ns/op	       0 B/op	       0 allocs/op
BenchmarkSyncMeasure/NoView/Float64Gauge/Attributes/10-24        	   41348	       291.0 ns/op	       0 B/op	       0 allocs/op
BenchmarkSyncMeasure/NoView/Int64Gauge/Attributes/0-24         	   48070	       291.1 ns/op	       0 B/op	       0 allocs/op
BenchmarkSyncMeasure/NoView/Int64Gauge/Attributes/1-24         	   43290	       274.9 ns/op	       0 B/op	       0 allocs/op
BenchmarkSyncMeasure/NoView/Int64Gauge/Attributes/10-24        	   40003	       325.0 ns/op	       0 B/op	       0 allocs/op

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 85.5%. Comparing base (97e2244) to head (e71e40c).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@          Coverage Diff          @@
##            main   #7407   +/-   ##
=====================================
  Coverage   85.5%   85.5%           
=====================================
  Files        277     277           
  Lines      24644   24644           
=====================================
  Hits       21076   21076           
  Misses      3189    3189           
  Partials     379     379           

see 2 files with indirect coverage changes

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[dashpole]

Merging early since it is trivial