Stop validating View-provided stream name against instrument name syntax

[cijothomas]

Per the OpenTelemetry specification clarification in open-telemetry/opentelemetry-specification#5094, the View-provided stream name is NOT subject to the instrument name syntax and the SDK MUST NOT validate it against that syntax.

Removes the name-syntax validation (empty / length / first-char-alpha / allowed-chars) from StreamBuilder::build(). unit, cardinality limit, and histogram-bucket validation are unchanged. Direct instrument creation via Meter continues to enforce the syntax.

Spec PR: open-telemetry/opentelemetry-specification#5094

[codecov]

Codecov Report

❌ Patch coverage is 95.23810% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 82.8%. Comparing base (8db5a12) to head (a844102).

Files with missing lines	Patch %	Lines
opentelemetry-sdk/src/metrics/instrument.rs	95.2%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##            main   #3518     +/-   ##
=======================================
- Coverage   82.8%   82.8%   -0.1%     
=======================================
  Files        130     130             
  Lines      27289   27262     -27     
=======================================
- Hits       22622   22595     -27     
  Misses      4667    4667             

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