w3c tracecontext: Add traceparent randomness bit tests

[mabdinur]

Motivation

Add test coverage for the W3C trace-context-2 spec's randomness bit (bit 1) in trace flags to ensure:

1. Setting the randomness bit doesn't break sampling decisions (only bit 0 determines sampling)
2. New Datadog traces properly set the randomness bit to 1
3. The randomness bit is propagated correctly when extracting headers

Changes

• Added test_traceparent_trace_flags_sampling_with_randomness_bit: Verifies only bit 0 determines sampling, regardless of bit 1
• Added test_traceparent_trace_flags_randomness_bit_new_trace: Tests new Datadog traces have randomness bit set to 1
• Added test_traceparent_trace_flags_randomness_bit_propagation: Tests randomness bit propagation when extracting headers
• Added skip entries to all language manifest files for the randomness bit tests (not supported yet)
• Fixed parametric apps (PHP, Node.js, Ruby, Rust) to return SDK trace_flags as 2-digit hex instead of custom logic that only checked sampled bit

Workflow

1. ⚠️ Create your PR as draft ⚠️
2. Work on you PR until the CI passes
3. Mark it as ready for review
   • Test logic is modified? -> Get a review from RFC owner.
   • Framework is modified, or non obvious usage of it -> get a review from R&P team

🚀 Once your PR is reviewed and the CI green, you can merge it!

🛟 #apm-shared-testing 🛟

Reviewer checklist

• Anything but tests/ or manifests/ is modified ? I have the approval from R&P team
• A docker base image is modified?
  • the relevant build-XXX-image label is present
• A scenario is added, removed or renamed?
  • Get a review from R&P team

[github-actions]

CODEOWNERS have been resolved as:

manifests/cpp.yml                                                       @DataDog/dd-trace-cpp
manifests/dotnet.yml                                                    @DataDog/apm-dotnet @DataDog/asm-dotnet
manifests/golang.yml                                                    @DataDog/dd-trace-go-guild
manifests/java.yml                                                      @DataDog/asm-java @DataDog/apm-java
manifests/nodejs.yml                                                    @DataDog/dd-trace-js
manifests/php.yml                                                       @DataDog/apm-php @DataDog/asm-php
manifests/python.yml                                                    @DataDog/apm-python @DataDog/asm-python
manifests/ruby.yml                                                      @DataDog/ruby-guild @DataDog/asm-ruby
manifests/rust.yml                                                      @DataDog/apm-rust
tests/parametric/test_headers_tracecontext.py                           @DataDog/system-tests-core @DataDog/apm-sdk-capabilities
utils/build/docker/nodejs/parametric/server.js                          @DataDog/dd-trace-js @DataDog/system-tests-core
utils/build/docker/php/parametric/server.php                            @DataDog/apm-php @DataDog/system-tests-core
utils/build/docker/ruby/parametric/server.rb                            @DataDog/ruby-guild @DataDog/asm-ruby @DataDog/system-tests-core
utils/build/docker/rust/parametric/src/opentelemetry/mod.rs             @DataDog/apm-rust @DataDog/system-tests-core