refactor: use match cases for workflow stream responses

[D-393Patel]

Summary

#35902

Refactors workflow stream response conversion to use Python match cases instead of isinstance branching.

Updated:

• api/core/app/apps/workflow/generate_response_converter.py
• api/core/app/apps/pipeline/generate_response_converter.py

Behavior is unchanged for:

• ping events
• error events
• node start/finish events
• default stream events

From Codex

Screenshots

Before	After
Not applicable, backend refactor only.	Not applicable, backend refactor only.

Checklist

• This change requires a documentation update, included: Dify Document
• I understand that this PR may be closed in case there was no previous discussion or issues. (This doesn't apply to typos!)
• I've added a test for each change that was introduced, and I tried as much as possible to make a single atomic change.
• I've updated the documentation accordingly.
• I ran make lint && make type-check (backend) and cd web && pnpm exec vp staged (frontend) to appease the lint gods

Testing:

• Ran py -3 -m py_compile api/core/app/apps/workflow/generate_response_converter.py api/core/app/apps/pipeline/generate_response_converter.py

Could not run the full backend test/lint suite locally because uv is not installed on PATH and local Python does not have pytest.

[github-actions]

Pyrefly Type Coverage

Metric	Base	PR	Delta
Type coverage	0.00%	43.70%	+43.70%
Strict coverage	0.00%	43.22%	+43.22%
Typed symbols	0	22,132	+22,132
Untyped symbols	0	28,831	+28,831
Modules	0	2557	+2,557

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