docs: Fix and complete numpydoc Parameters sections

[xuanku-001]

Summary

Fixes and completes numpydoc Parameters sections in the container and event APIs:

• connect_child_events: the section header was written as Parameters. (with a
  trailing period), which numpydoc does not recognize, so the parameter list below it
  was rendered as plain text.
• qt.stop_emitting_from_queue: the parameter list (thread) had no Parameters
  header at all.
• SelectableEventedList.select_previous: select_next right above it documents
  expand_selection and wraparound; select_previous takes the same arguments but
  had no section. The new section mirrors the existing one.
• SelectableEventedList.insert, EventedList.reverse, SignalRelay.block, and
  Selectable.selection: their parameters were not described.

All existing sentences are preserved verbatim; only sections are added, so no
behaviour or signatures change. These docstrings are rendered on the docs site with
docstring_style: numpy, so the two header fixes directly affect the rendered API
reference (the previously broken lists are currently shown as plain text).

Testing

• python -m py_compile passes on all touched files
• AST statement counts are unchanged (documentation only, no executable lines added)
• All parameter names cross-checked against signatures (ruff D417-consistent), and
  the section headers follow the existing Parameters / ---------- pattern used
  elsewhere in the codebase

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This contribution was prepared with AI assistance (a local LLM-based agent harness with deterministic checks and human review).

[codspeed]

Merging this PR will not alter performance

✅ 67 untouched benchmarks

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_{Comparing xuanku-001:docs/numpydoc-params-sections (b261969) with main (49670f8)}