feat(heap-profiling): expose libdatadog heap profiling primitive to users [PROF-15190]

[scottgerring]

Warning

This PR is still a draft pending merging of the libdatadog work.

What does this PR do?

The profiling team is adding heap profiling support to libdatadog and the eBPF full host profiler. This works by exposing a USDT behind a sampled allocation path, so that the profiler can hook profiled applications to obtain statistically significant heap samples without having to hook every allocation. In the Rust case, this is supported by providing a GlobalAllocator wrapper.

Additional Notes

once libdatadog is in, are we happy to merge this into dd-trace-rs (perhaps behind an experimental flag) before we upstream it into the full host profiler, or would we rather carry it on a branch?

[datadog-prod-us1-6]

🎉 All green!

🧪 All tests passed
❄️ No new flaky tests detected

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[Copilot]

Pull request overview

Adds an opt-in “memory profiling” capability to datadog-opentelemetry by exposing libdatadog’s sampled heap-allocation allocator wrapper behind a feature flag, enabling out-of-process profilers to collect allocation samples via USDT probes.

Changes:

• Introduces a new memory_profiling module that re-exports libdd_heap_allocator::SampledAllocator and provides a minimal builder-style opt-in API.
• Wires the module behind a new memory-profiling crate feature and documents the feature in crate-level docs.
• Adds a temporary git dependency on an in-progress libdatadog branch and updates the lockfile accordingly.

Reviewed changes

Copilot reviewed 4 out of 5 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
datadog-opentelemetry/src/memory_profiling.rs	New public module documenting allocator-based opt-in and providing the builder API.
datadog-opentelemetry/src/lib.rs	Documents and conditionally exposes the memory_profiling module + entrypoint under a feature flag.
datadog-opentelemetry/Cargo.toml	Adds optional libdd-heap-allocator dependency and memory-profiling feature.
Cargo.toml	Adds workspace dependency pointing to a libdatadog git branch for the new allocator crate.
Cargo.lock	Locks the newly introduced git-based libdatadog crates and their transitive deps (e.g., bindgen).

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