Fix callbacks registered twice under reload when Dash() gets an explicit name

[raashish1601]

Dash.__init__ passed caller_name to alias_main_module. When name is given, caller_name is that name. So Dash("myapp"), or Dash(__name__) inside an app factory module, never matched "__main__"/"__mp_main__". The alias was skipped, uvicorn's "repro:server" import ran the file again, and every callback was registered twice.

Now the alias uses get_caller_name(), the module that is actually running, whatever name is. The app name (caller_name) is unchanged. In the factory case the running module is the entry script that calls the factory, so that script gets aliased.

Tested:

• Two new tests in tests/unit/test_main_module_alias.py: explicit name, and an app built by a factory called from the main module. Both fail on dev and pass here.
• Ran the repro from the issue with uvicorn.run(..., reload=True). /_dash-dependencies lists output.children twice on dev, once with this change.
• pytest tests/unit: the only failures are the test_pages.py path tests, test_pages_config.py and test_process_server_smoke. They fail the same way on dev on my Windows machine. pylint, flake8 and black pass on the changed files.

Contributor Checklist

• I have broken down my PR scope into the following TODO tasks
  • Alias the running main module even when Dash() gets an explicit name
  • Add regression tests for the explicit-name and app-factory cases
• I have run the tests locally and they passed. (refer to testing section in contributing)
• I have added tests, or extended existing tests, to cover any new features or bugs fixed in this PR

optionals

• I have added entry in the CHANGELOG.md

Fixes #3912

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[raashish1601]

The "Run performance benchmarks" failure isn't from this change. The benchmarks themselves report all within thresholds. The job then fails when it tries to post its results comment (HttpError: Resource not accessible by integration), since the PR comes from a fork. Dash Testing passed.