tracer: discard invalid _dd.p.tid in the datadog propagator

[ahmed-mez]

What does this PR do?

• Do not set _dd.p.tid in the datadog propagator if the value isn't valid
• Inspired by ddtrace/tracer/textmap: Setting _dd.propagation_error tag on faulty context propagation #1969
• This doesn't cover malformed tid in the tracecontext propagator: keep sending the malformed tid seems to be the expected behavior in that case, based on the parametric tests
• This doesn't cover sending the optional _dd.propagation_error tag

Motivation

Enable test case test_datadog_128_bit_propagation_tid_short in parametric tests https://github.com/DataDog/system-tests/blob/main/tests/parametric/test_128_bit_traceids.py#L76

Describe how to test/QA your changes

Unit tests + test case in parametric tests is enabled once this PR is merged

Reviewer's Checklist

• Changed code has unit tests for its functionality.
• If this interacts with the agent in a new way, a system test has been added.

[pr-commenter]

Benchmarks

Benchmark execution time: 2023-06-27 09:59:13

Comparing candidate commit d183422 in PR branch ahmed/tid-validation with baseline commit 12ed8da in branch main.

Found 0 performance improvements and 0 performance regressions! Performance is the same for 24 metrics, 0 unstable metrics.