[ENH] Reduce complexity of run_flow_on_task func

[Omswastik-11]

Summary

This PR refactors run_flow_on_task, which had grown to ~160 lines with high cyclomatic complexity, by extracting small helper functions with clear, single responsibilities. The main function is now a readable orchestrator with clearly defined steps.

---

Changes

Extracted helper functions

• _validate_flow_and_task_inputs
  Handles input validation and backward-compatible argument handling

• _sync_flow_with_server
  Synchronizes the flow with the server and checks for duplicate runs

• _prepare_run_environment
  Prepares environment information and run tags

• _create_run_from_results
  Builds the OpenMLRun object from execution results

Internal structure improvements

• Introduced a _RunResults NamedTuple to bundle execution outputs
  (data_content, trace, evaluations) and reduce long parameter lists

---

Type Safety Improvements

• Replaced assert statements with explicit ValueError / TypeError exceptions
• Added type guards before accessing attributes that may be None
• Made boolean parameters keyword-only where appropriate

---

Fixes #1580

[codecov-commenter]

Codecov Report

❌ Patch coverage is 15.27778% with 61 lines in your changes missing coverage. Please review.
✅ Project coverage is 66.06%. Comparing base (3454bbb) to head (5a4a089).

Files with missing lines	Patch %	Lines
openml/runs/functions.py	15.27%	61 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #1596       +/-   ##
===========================================
+ Coverage   52.72%   66.06%   +13.34%     
===========================================
  Files          36       36               
  Lines        4326     4353       +27     
===========================================
+ Hits         2281     2876      +595     
+ Misses       2045     1477      -568     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.