test(examples): retry background sidecar on transient port-bind flake

[kshitizj03]

Description

test_demo_actor flakes when the demo-actor sidecar, started via DaprRunner.start(), loses a random-port race at boot: daprd assigns the same port to its API and internal gRPC servers, the internal listener fails with "bind: address already in use", and the runtime exits with "could not listen on any endpoint". The actor host is then dead, so the client's invoke_method fails with "did not find address for actor" and the expected output never appears.

PR #1030 already added this retry to the foreground run() path, but the background start() path was left uncovered. This applies the same exponential backoff retry there, reusing the existing failure markers. The captured log is only read once the process has exited (poll() is not None), so a healthy long-lived sidecar is never inspected and its append offset is left untouched.

Adds unit tests mirroring the existing run() coverage.

Fixes #1061

Checklist

Please make sure you've completed the relevant tasks for this PR, out of the following list:

• Code compiles correctly
• Created/updated tests
• Extended the documentation

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 82.15%. Comparing base (bffb749) to head (da1b63b).
⚠️ Report is 148 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1101      +/-   ##
==========================================
- Coverage   86.63%   82.15%   -4.48%     
==========================================
  Files          84      116      +32     
  Lines        4473     9578    +5105     
==========================================
+ Hits         3875     7869    +3994     
- Misses        598     1709    +1111     

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[Copilot]

Pull request overview

This PR reduces flakes in the examples test suite by making DaprRunner.start() resilient to a known transient Dapr sidecar startup failure (random-port bind collision), mirroring the retry behavior already implemented for DaprRunner.run().

Changes:

• Add exponential-backoff retry logic to DaprRunner.start() when startup output matches the existing port-bind failure markers.
• Add unit tests covering the retry and non-retry paths for start() using a background-process stand-in.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
tests/examples/conftest.py	Adds port-bind collision retry logic to DaprRunner.start() and introduces a helper to detect the failure safely for background sidecars.
tests/examples/test_dapr_runner.py	Adds unit tests for start() retry behavior and introduces a fake background process for deterministic output simulation.

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[marcduiker]

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