all: replace internal/telemetry by internal/newtelemetry

[eliottness]

What does this PR do?

This PR replace the old telemetry client with the new one. It does, in order:

• git rm -r internal/telemetry
• git mv internal/newtelemetry internal/telemetry
• Apply changes on the parts of the API that changed signicantly:
  • The way to start a new telemetry client is different, no more telemetry.ApplyOps
  • The API for metrics has been changed for better performances
• Rework the internal/telemetry/telemetrytest package because it was not using github.com/stretchr/testify/mock correctly (like, not at all)
• Update a literral TON of tests that were using the horrible telemetrytest API

Motivation

Better telemetry and support for telemetry metrics in the customer request hot path.
RFC: https://docs.google.com/document/d/1C3xoTZHQZNQ-Jr1w5mMThIkpHNW_4qKRf-J5CNi7G-k/edit?pli=1&tab=t.0#heading=h.88xvn2cvs9dt

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.
• 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.
• For internal contributors, a matching PR should be created to the v2-dev branch and reviewed by @DataDog/apm-go.

Unsure? Have a question? Request a review!

[datadog-datadog-prod-us1]

Datadog Report

Branch report: eliott.bouhana/remove-oldtelemetry
Commit report: 02366fc
Test service: dd-trace-go

✅ 0 Failed, 5298 Passed, 72 Skipped, 1m 55.88s Total Time

[pr-commenter]

Benchmarks

Benchmark execution time: 2025-02-07 17:02:33

Comparing candidate commit addfaa8 in PR branch eliott.bouhana/remove-oldtelemetry with baseline commit 3dd727b in branch eliott.bouhana/newtelemetry.

Found 0 performance improvements and 5 performance regressions! Performance is the same for 56 metrics, 1 unstable metrics.

scenario:BenchmarkOTelApiWithCustomTags/otel_api-24

• 🟥 allocated_mem [+448 bytes; +460 bytes] or [+9.244%; +9.487%]
• 🟥 allocations [+9; +9] or [+20.930%; +20.930%]
• 🟥 execution_time [+502.455ns; +562.545ns] or [+6.934%; +7.763%]

scenario:BenchmarkSetTagString-24

• 🟥 execution_time [+2.552ns; +5.128ns] or [+2.273%; +4.567%]

scenario:BenchmarkStartRequestSpan-24

• 🟥 execution_time [+10.501ns; +11.639ns] or [+2.888%; +3.201%]