Stop validating instrument unit

[jack-berg]

Spec PR #3171 clears up previous ambiguity in the spec around whether SDKs are supposed validate instrument unit.

Its now quite clear that the expectations about unit are for callers. The SDK itself is supposed to treat the value as an opaque string:

When a Meter creates an instrument, it SHOULD NOT validate the instrument unit.

This is in contrast to instrument name, which the SDK is supposed to validate:

When a Meter creates an instrument, it SHOULD validate the instrument name
conforms to the instrument name syntax

Also took it upon myself to suppress some new test logs that have popped up after recent commits.

[codecov]

Codecov Report

Patch coverage: 92.30% and project coverage change: -0.03 ⚠️

Comparison is base (2babc69) 90.98% compared to head (ce71a4c) 90.96%.

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #5279      +/-   ##
============================================
- Coverage     90.98%   90.96%   -0.03%     
+ Complexity     4908     4897      -11     
============================================
  Files           552      551       -1     
  Lines         14489    14475      -14     
  Branches       1372     1368       -4     
============================================
- Hits          13183    13167      -16     
- Misses          906      909       +3     
+ Partials        400      399       -1     

Impacted Files	Coverage Δ
...in/java/io/opentelemetry/sdk/metrics/SdkMeter.java	98.03% <90.90%> (-1.97%)	⬇️
.../io/opentelemetry/api/internal/ApiUsageLogger.java	100.00% <100.00%> (ø)
...lemetry/sdk/metrics/AbstractInstrumentBuilder.java	100.00% <100.00%> (+2.08%)	⬆️

... and 4 files with indirect coverage changes

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