[EXPORTER] Convert uint64_t attribute values exceeding INT64_MAX to s…

[malkia]

…tring per OTel spec (open-telemetry#4090)

Per OpenTelemetry attribute type-mapping spec (https://opentelemetry.io/ docs/specs/otel/common/attribute-type-mapping/#integer-values), integer values outside the 64-bit signed range MUST be encoded as AnyValue's string_value using decimal representation, not wrapped to a negative int64 via narrowing.

Pre-PR behavior at the four uint64_t conversion sites in otlp_populate_attribute_utils.cc was to implicitly narrow (suppressed via NOLINT). For uint64_t values exceeding INT64_MAX, this produced negative int_value on the wire — a long-standing spec violation that predates this PR.

This PR fixes the violation via a file-local helper SetUint64Value that dispatches to set_int_value or set_string_value based on the value's range. All four uint64_t sites in both PopulateAnyValue overloads now follow the spec.

Spec-compliance verified by three new tests in otlp_recordable_test.cc:

• UINT64_MAX-equivalent value -> string_value with decimal representation
• INT64_MAX boundary value -> int_value (encoding split is val > INT64_MAX)
• Mixed-value array -> per-element dispatch (int + string in same array)

Side effect: the four bugprone-narrowing-conversions warnings clang-tidy v22 was reporting are eliminated (the static_cast is now in a guarded branch, suppressing the diagnostic). Ratchet drops accordingly:

• abiv1-preview warning_limit lowered from 389 to 385
• abiv2-preview warning_limit lowered from 395 to 391

Behavior change: existing callers relying on the wrap-to-negative behavior for uint64 > INT64_MAX will now see string_value on the wire instead of negative int_value. This was never spec-conformant; the new behavior aligns OTLP output with the protocol specification.

Part of open-telemetry#2053

Fixes # (issue)

Changes

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For significant contributions please make sure you have completed the following items:

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