internal/datastreams: add process tags to dsm payloads

[rarguelloF]

What does this PR do?

Followup of #3566

Adds ProcessTags to DSM payloads.

(needed to update the hashing logic to include process tags as well).

Motivation

Reviewer's Checklist

• Changed code has unit tests for its functionality at or near 100% coverage.
• System-Tests covering this feature have been added and enabled with the va.b.c-dev version tag.
• There is a benchmark for any new code, or changes to existing code.
• If this interacts with the agent in a new way, a system test has been added.
• New code is free of linting errors. You can check this by running golangci-lint run locally.
• Add an appropriate team label so this PR gets put in the right place for the release notes.
• Non-trivial go.mod changes, e.g. adding new modules, are reviewed by @DataDog/dd-trace-go-guild.

Unsure? Have a question? Request a review!

[pr-commenter]

Benchmarks

Benchmark execution time: 2025-06-06 15:58:32

Comparing candidate commit 03e5301 in PR branch rarguelloF/process-tags-dsm with baseline commit 5ea1efb in branch main.

Found 0 performance improvements and 0 performance regressions! Performance is the same for 21 metrics, 0 unstable metrics.

[piochelepiotr]

Main question about performance. Is there a way to add a RW lock on the value of process tags, and then copy on write if the value is changed?
I want to make sure the SetCheckpoint method is not impacted performance wise.

[rarguelloF]

@piochelepiotr Leaving here the benchmarks for posterity:

Ran the existing benchmark on my machine:

// 1st run

goos: darwin
goarch: arm64
pkg: github.com/DataDog/dd-trace-go/v2/internal/datastreams
cpu: Apple M1 Max
BenchmarkSetCheckpoint
BenchmarkSetCheckpoint-10    	 3214754	       374.0 ns/op
PASS

Process finished with the exit code 0

// 2nd run

goos: darwin
goarch: arm64
pkg: github.com/DataDog/dd-trace-go/v2/internal/datastreams
cpu: Apple M1 Max
BenchmarkSetCheckpoint
BenchmarkSetCheckpoint-10    	 3276264	       365.8 ns/op
PASS

Process finished with the exit code 0

New benchmark enabling process tags:

// 1st run

goos: darwin
goarch: arm64
pkg: github.com/DataDog/dd-trace-go/v2/internal/datastreams
cpu: Apple M1 Max
BenchmarkSetCheckpointProcessTags
BenchmarkSetCheckpointProcessTags-10    	 3170246	       376.6 ns/op
PASS

Process finished with the exit code 0

// 2nd run

goos: darwin
goarch: arm64
pkg: github.com/DataDog/dd-trace-go/v2/internal/datastreams
cpu: Apple M1 Max
BenchmarkSetCheckpointProcessTags
BenchmarkSetCheckpointProcessTags-10    	 3138550	       372.7 ns/op
PASS

Process finished with the exit code 0

Tested a version of processtags using atomic instead of RWMutex:

goos: darwin
goarch: arm64
pkg: github.com/DataDog/dd-trace-go/v2/internal/datastreams
cpu: Apple M1 Max
BenchmarkSetCheckpointProcessTags
BenchmarkSetCheckpointProcessTags-10    	 3209713	       368.0 ns/op
PASS

Process finished with the exit code 0

In the end I left it the same as it is because there are no notable differences.