[dynamic control] add TraceSamplingRateValidator

[jackshirazi]

Description:

TraceSamplingRatePolicy is implemented to use ratio, a value between 0-1. While this is technically correct, the examples in the telemetry policy spec provide percentages, and it's clear that both ratios and percentages need to be supported. The cleanest way to do this is to provide two policies which share the same behaviour except for naming and value conversion. Implementation is best done by abstracting common behaviour and providing minimal implementations of concrete subclasses. This is the next step to achieve that.

Existing Issue(s):

#2868

Testing:

Included

Documentation:

To be added

Outstanding items:

Expected set of PRs:

• DONE: trace sampling policy refactored to abstract superclass and concrete class [dynamic control] refactor TraceSamplingRatePolicy to allow percent and ratio #3050
• DONE: validator refactored to abstract superclass and concrete class [dynamic control] Trace sampling validator refactored to abstract superclass and concrete class #3070
• DONE: integrate the validators to policy wiring [dynamic control] Integrate the validators to policy wiring #3071
• THIS PR (part1) create/convert the ratio/percentage policy concrete classes
• add docs
• cleanup (a bit of renaming)

also #2868

[Copilot]

Pull request overview

Adds a new trace sampling validator intended to parse ratio-shaped configurations (e.g., {"trace-sampling":{"ratio":0.75}}) as part of the dynamic-control trace sampling policy evolution.

Changes:

• Introduces TraceSamplingRateValidator (ratio keyword) as an AbstractTraceSamplingValidator specialization.
• Adds TraceSamplingRateValidatorTest covering flat numeric, ratio keyword JSON, and key-value parsing.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
dynamic-control/src/main/java/io/opentelemetry/contrib/dynamic/policy/tracesampling/TraceSamplingRateValidator.java	New validator that parses ratio keyword / numeric values into TraceSamplingRatePolicy.
dynamic-control/src/test/java/io/opentelemetry/contrib/dynamic/policy/tracesampling/TraceSamplingRateValidatorTest.java	New unit tests validating ratio parsing and rejection cases.

Suppressed comments (1)

dynamic-control/src/main/java/io/opentelemetry/contrib/dynamic/policy/tracesampling/TraceSamplingRateValidator.java:33

• The log message uses "sampling-rate" terminology, but this validator is for the trace-sampling policy type. Aligning the message with the actual policy type makes operational logs easier to interpret.

    try {
      return new TraceSamplingRatePolicy(ratio, sourceKind);
    } catch (IllegalArgumentException e) {
      logger.info("Invalid sampling-rate ratio '" + ratio + "' will be ignored: " + e.getMessage());
      return null;

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