tests: raise eventstream coverage from 65% to 75%

[TeoSlayer]

Summary

Adds focused tests for previously uncovered broker and server branches. No production code changes — single new file zz_added_coverage_test.go.

Coverage delta:

• package eventstream: 77.1% -> 89.2%
• module total (incl. examples/): 65.2% -> 75.4%

Per-function highlights:

• server.handleConn 0% -> 100%
• service.Stop 88.9% -> 100%
• broker.handleConn 72.4% -> 100%
• publishWith 89.7% -> 100%
• takeToken 94.7% -> 100%

What the tests cover

• Server.handleConn full subscribe/publish/cleanup with net.Pipe connections
• Server.publish wildcard sender-skipped + topic literal * no-double-deliver branches
• broker.handleConn subscribe-read-fail early-return path
• All four pubsub bus event branches (pubsub.subscribed, pubsub.unsubscribed, pubsub.published, pubsub.rate_limited) via a recording stub EventBus
• broker.publishWith wildcard fan-out, sender-skip on wildcard, and topic-is-wildcard skip branch
• Service.Stop ctx.Done() early-return when shutdown blocks
• takeToken refill clamp at publishBurstBudget

Approach: a pipeStream adapter wires net.Pipe into coreapi.Stream, letting broker.handleConn run end-to-end without a real driver/tunnel. Same trick (raw net.Pipe) drives Server.handleConn since it takes net.Conn directly.

Test plan

• go test -race -count=1 -timeout 120s ./... passes
• go vet ./... clean
• go tool cover -func confirms 75.4% module / 89.2% package

[codecov]

Welcome to Codecov 🎉

Once you merge this PR into your default branch, you're all set! Codecov will compare coverage reports and display results in all future pull requests.

ℹ️ You can also turn on project coverage checks and project coverage reporting on Pull Request comment

Thanks for integrating Codecov - We've got you covered ☂️