[SDK] Add missing cstdint include to predicate_factory.h

[om7057]

Fixes # (issue)

Changes

predicate_factory.h declares enum class PredicateType : uint8_t and uses uint8_t without including <cstdint>. It compiles today only because something else in the same translation unit happens to pull that header in transitively. Building it in isolation, or under a standard library that no longer provides that transitive include, fails to compile. This adds the missing #include <cstdint> directly to the header that needs it.

• CHANGELOG.md updated for non-trivial changes
• Unit tests have been added
• Changes in public API reviewed

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.51%. Comparing base (1a27841) to head (f920bfc).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4574      +/-   ##
==========================================
- Coverage   86.52%   86.51%   -0.00%     
==========================================
  Files         525      525              
  Lines       20464    20464              
==========================================
- Hits        17704    17702       -2     
- Misses       2760     2762       +2     

Files with missing lines	Coverage Δ
...opentelemetry/sdk/metrics/view/predicate_factory.h	90.91% <ø> (ø)

... and 1 file with indirect coverage changes

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[lalitb]

LGTM, thanks for the fix. Also good to open a follow-up issue to extend our IWYU checks to headers without a matching .cc file. We can handle that separately.