Remove unnecessary python version checks.

[brandonschabell]

Remove unnecessary Python version checks (pre 3.9).

Also switched from typing_extensions to typing imports for types that were added to the typing library as of 3.9.

Contributor Checklist

• I have broken down my PR scope into the following TODO tasks
  • task 1
  • task 2
• 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
• If this PR needs a follow-up in dash docs, community thread, I have mentioned the relevant URLS as follows
  • this GitHub #PR number updates the dash docs
  • here is the show and tell thread in Plotly Dash community

[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

[Copilot]

Copilot review overview

🟢 Approval recommended

The mechanical cleanup matches the declared Python 3.9 minimum and preserves required compatibility imports.

Review effort: Balanced
Findings: None

What changed in this PR

Removes obsolete checks for Python versions below the supported minimum of 3.9 and adopts standard-library typing APIs where compatible.

Changes:

• Removed obsolete test skip markers and imports.
• Replaced compatible typing_extensions imports with typing.
• Simplified JSON loading and CI dependency conditions.

File	Description
tests/​unit/​test_app_runners.py	Removes a Python 2 skip condition.
tests/​background_callback/​test_basic_long_callback016.py	Removes the pre-3.9 skip condition.
tests/​background_callback/​test_basic_long_callback015.py	Removes the legacy version skip.
tests/​background_callback/​test_basic_long_callback014.py	Removes the legacy version skip.
tests/​background_callback/​test_basic_long_callback013.py	Removes the legacy version skip.
tests/​background_callback/​test_basic_long_callback012.py	Removes the legacy version skip.
tests/​background_callback/​test_basic_long_callback011.py	Removes the legacy version skip.
tests/​background_callback/​test_basic_long_callback010.py	Removes the legacy version skip.
tests/​background_callback/​test_basic_long_callback009.py	Removes the legacy version skip.
tests/​background_callback/​test_basic_long_callback008.py	Removes the legacy version skip.
tests/​background_callback/​test_basic_long_callback007.py	Removes the legacy version skip.
tests/​background_callback/​test_basic_long_callback006.py	Removes the legacy version skip.
tests/​background_callback/​test_basic_long_callback005.py	Removes the version skip while retaining the timeout skip.
tests/​background_callback/​test_basic_long_callback004.py	Removes the legacy version skip.
tests/​background_callback/​test_basic_long_callback003.py	Removes the legacy version skip.
tests/​background_callback/​test_basic_long_callback002.py	Removes the legacy version skip.
tests/​background_callback/​test_basic_long_callback001.py	Removes the legacy version skip.
tests/​async_tests/​test_async_background_callbacks.py	Removes the legacy callback-test skip.
requirements/​ci.txt	Installs Pyright without an obsolete version marker.
dash/​types.py	Imports Annotated from typing.
dash/​resources.py	Uses the standard-library TypedDict.
dash/​mcp/​primitives/​tools/​tool_get_dash_component.py	Imports Annotated from typing.
dash/​development/​component_generator.py	Removes the Python 2 JSON conversion path.
dash/​_jupyter.py	Imports Literal from typing.
dash/​_hooks.py	Uses standard-library typing primitives.
components/​dash-core-components/​tests/​integration/​store/​test_store_data.py	Removes an obsolete pre-3.6 skip.
CHANGELOG.md	Records removal of pre-3.9 checks.

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