SD-11577: add worker subrequest support

[rtalvarez]

Pull Request Template

Description

• Add worker subrequests metrics via Cloudflare's workersSubrequestsAdaptiveGroups GraphQL dataset
• New metric cloudflare_worker_subrequests_count — subrequest count per script name
• New metric cloudflare_worker_subrequest_time — response time quantiles (P50/P75/P99/P999) in microseconds per script name
• Both metrics support the denylist and follow existing patterns (structs, registration, goroutine wiring)
• README updated with new metrics

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Code refactoring
• Other (please describe):

Testing

Ran the app locally and verified the graphql query is executed correctly for workersSubrequestsAdaptiveGroups

DEBUG[2026-03-19 08:30:00] func:main.NewGraphQLClient.func1 file:graphql.go >> query: query ($accountID: String!, $mintime: Time!, $maxtime: Time!, $limit: Int!) { viewer { accounts(filter: {accountTag: $accountID}) { workersSubrequestsAdaptiveGroups(limit: $limit, filter: {datetime_geq: $mintime, datetime_lt: $maxtime}) { dimensions { scriptName } sum { subrequests } quantiles { timeToResponseUsP50 timeToResponseUsP75 timeToResponseUsP99 timeToResponseUsP999 } } } } }

Visiting localhost:8080/metrics locally, i can see both cloudflare_worker_subrequest_time and cloudflare_worker_subrequests_count

Code Quality

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation

Before Submitting

Please ensure you have completed the following before submitting your PR:

# Run comprehensive tests
make pr-tests

If the above command fails, please fix the issues before submitting your PR.

Additional Notes

Add any other context about the pull request here.

[chanceaclark]

This is going to be nice for observability purposes