Remove the use of metric/unit

[MadVikingGod]

This updates our use of metric/unit in tests and examples. This is because metric/unit was deprecated in open-telemetry/opentelemetry-go#3776

[codecov]

Codecov Report

Merging #3509 (baf3909) into main (e054521) will increase coverage by 2.9%.
The diff coverage is 9.0%.

Additional details and impacted files

@@           Coverage Diff           @@
##            main   #3509     +/-   ##
=======================================
+ Coverage   69.9%   72.9%   +2.9%     
=======================================
  Files        147     149      +2     
  Lines       6934    6980     +46     
=======================================
+ Hits        4851    5092    +241     
+ Misses      1959    1751    -208     
- Partials     124     137     +13     

Impacted Files	Coverage Δ
...entation/google.golang.org/grpc/otelgrpc/config.go	65.1% <0.0%> (ø)
instrumentation/host/host.go	0.0% <0.0%> (ø)
instrumentation/runtime/runtime.go	0.0% <0.0%> (ø)
...ion/github.com/gocql/gocql/otelgocql/instrument.go	62.5% <100.0%> (+62.5%)	⬆️
...n/github.com/gocql/gocql/otelgocql/test/version.go	0.0% <0.0%> (ø)
.../github.com/gocql/gocql/otelgocql/internal/cass.go	95.1% <0.0%> (ø)
...ntation/github.com/gocql/gocql/otelgocql/config.go	67.3% <0.0%> (+67.3%)	⬆️
...ation/github.com/gocql/gocql/otelgocql/observer.go	75.1% <0.0%> (+75.1%)	⬆️
...entation/github.com/gocql/gocql/otelgocql/gocql.go	100.0% <0.0%> (+100.0%)	⬆️
... and 1 more