contrib/valyala/fasthttp.v1: add a fasthttp integration to ddtrace

[mtoffl01]

What does this PR do?

Provides middleware to trace requests handled with the FastHTTP library: https://pkg.go.dev/github.com/valyala/fasthttp

Motivation

Customer requests!
#700

Reviewer's Checklist

• Changed code has unit tests for its functionality at or near 100% coverage.
• 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.

For Datadog employees:

• [] If this PR touches code that handles credentials of any kind, such as Datadog API keys, I've requested a review from @DataDog/security-design-and-guidance.
• This PR doesn't touch any of that.

Unsure? Have a question? Request a review!

[pr-commenter]

Benchmarks

Benchmark execution time: 2023-12-18 10:24:25

Comparing candidate commit a083689 in PR branch mtoff/fasthttp with baseline commit e44bd72 in branch main.

Found 0 performance improvements and 0 performance regressions! Performance is the same for 40 metrics, 1 unstable metrics.

[mtoffl01]

The unit tests fail when run with -shuffle=on. They pass with -race and -parallel=N. For some reason, when they are run with shuffle, each test has an additional client net/http span, which I can't understand because the only test where I instrument the client call is TestPropagation.

Also, tests pass with the -shuffle=on flag if I comment out either TestPropagation or TestChildSpan 🤔
Can reproduce this issue running go test -shuffle=on inside of dd-trace-go/contrib/valyala/fasthttp.v1.

This is resolved in commit #43a2ed7.

[felixge]

The unit tests fail when run with -shuffle=on

Is this when running the tests for the new package you're adding, or the whole test suite? The latter doesn't work with -shuffle=on yet AFAIK, but it'd be great for new packages to pass with this flag enabled.

Let me know if you need help debugging.

[mtoffl01]

I want to make sure we add documentation for how to use the integration, like the example for net/http contrib - https://pkg.go.dev/gopkg.in/DataDog/dd-trace-go.v1/contrib/net/http#example-package

[github-actions]

This PR is stale because it has been open 20 days with no activity. Remove stale label or comment or this will be closed in 10 days.

[rarguelloF]

Nice work! 🎉

Left some refactor suggestions. Also we should make sure we add an example_test.go file with a ExampleWrapHandler function to make sure we provide documentation to users on how to use the integration.

[darccio]

/merge

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mergequeue build completed successfully, but the github api returned an error while merging the pr

Details

Error: PUT https://api.github.com/repos/DataDog/dd-trace-go/pulls/2305/merge: 405 5 of 5 required status checks are expected. []

FullStacktrace:
activity error (type: github.GithubService_MergePullRequest, scheduledEventID: 41, startedEventID: 42, identity: 1@github-worker-fb48fd8b7-zrxht@): PUT https://api.github.com/repos/DataDog/dd-trace-go/pulls/2305/merge: 405 5 of 5 required status checks are expected. [] (type: ErrorResponse, retryable: true)

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