dd-trace-rs: Unbounded W3C tracestate parsing may lead to DoS

dd-trace-rs provides Datadog application performance monitoring for Rust. From 0.1.0 until 0.3.3, datadog-opentelemetry/src/propagation/tracecontext.rs parses the W3C tracestate header and collects every semicolon-separated key and value pair in the Datadog dd=... vendor entry into a HashMap without enforcing a pair count or entry size limit. Because tracecontext extraction is enabled by default, a remote unauthenticated attacker can send an arbitrarily large dd=... entry and force excessive CPU and memory consumption for each request, causing denial of service in an instrumented network service. This vulnerability is fixed in 0.3.3.