docs: add summary lines to 9 field/name/parameter operation docstrings

[TaiSakuma]

Summary

Rolls the pilot from #3946 out to the 9 operations in the Field / name / parameter ops batch of #3980:

with_field, without_field, with_name, with_parameter, without_parameters, with_named_axis, without_named_axis, fields, parameters.

Each docstring now has:

• A one-line summary on the opening """.
• Returns: and Examples: section headers (the latter only where examples exist).

Original body text is preserved; only structural edits are applied. The summary lines were reviewed against the checklist posted in #3980.

Summary lines

Operation	Summary
ak.with_field	Returns an array or record with a new field added, or an existing field replaced.
ak.without_field	Returns an array or record with the named field removed.
ak.with_name	Returns an array or record with the __record__ parameter set to the given name.
ak.with_parameter	Returns an array with the given parameter set on the outermost layout node.
ak.without_parameters	Returns an array with all parameters removed from every layout node.
ak.with_named_axis	Returns an array with named axes attached.
ak.without_named_axis	Returns an array with named axes removed.
ak.fields	Returns a list of field names or tuple slot numbers for the outermost record.
ak.parameters	Returns the parameters dict of the outermost layout node.

Notes for reviewers

• Pre-existing bug surfaced (left verbatim in the body): ak.with_named_axis's narrative reads "…with a new name." — a copy-paste from ak_with_name.py. The function attaches named axes; the new summary says so. Happy to fix the body here or in a follow-up if you prefer.
• ak.with_field's "a new field added, or an existing field replaced" reflects the explicit replace-if-exists branch in _impl.
• ak.with_name keeps __record__ in backticks — it is the literal parameter key being set (the checklist's meaning-bearing exception).
• ak.without_parameters ("from every layout node") vs ak.with_parameter ("on the outermost layout node") is a real asymmetry in the implementations, not a mirroring defect.

Test plan

• pre-commit passes locally on the modified files (ruff check, ruff format, codespell, mypy).
• Mechanical validation: code outside docstrings byte-identical; Args: blocks and doctests byte-identical; no original narrative text lost.
• Sphinx docs build cleanly on CI.
• Rendered docstrings spot-checked in the docs preview.

Part of #3980. Draft for initial review; will mark ready once CI passes and the preview is checked.

AI assistance disclosure

Drafted with Claude Code: summaries drafted by Claude Sonnet 4.6, adversarially verified against the implementations by independent Claude Opus 4.8 agents, mechanically validated (docstring-only changes, original text preserved), and reviewed by a human before submission.

Co-Authored-By: Claude Sonnet 4.6 noreply@anthropic.com

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 83.74%. Comparing base (722a1b9) to head (6c4b5c3).
⚠️ Report is 14 commits behind head on main.

Additional details and impacted files

Files with missing lines	Coverage Δ
src/awkward/operations/ak_fields.py	100.00% <ø> (ø)
src/awkward/operations/ak_parameters.py	68.96% <ø> (ø)
src/awkward/operations/ak_with_field.py	100.00% <ø> (ø)
src/awkward/operations/ak_with_name.py	100.00% <ø> (ø)
src/awkward/operations/ak_with_named_axis.py	100.00% <ø> (ø)
src/awkward/operations/ak_with_parameter.py	100.00% <ø> (ø)
src/awkward/operations/ak_without_field.py	94.87% <ø> (ø)
src/awkward/operations/ak_without_named_axis.py	86.66% <ø> (ø)
src/awkward/operations/ak_without_parameters.py	100.00% <ø> (ø)

[TaiSakuma]

Follow-up per @ikrommyd's review on #4130: the Returns: sections now describe the returned object (a noun phrase) rather than restating the operation. Final Returns: lines for this batch:

Returns

Operation	Returns
ak.with_field	An #ak.Array or #ak.Record (or low-level equivalent, if highlevel=False) with a new field attached.
ak.without_field	An #ak.Array or #ak.Record (or low-level equivalent, if highlevel=False) with an existing field removed.
ak.with_name	An #ak.Array or #ak.Record (or low-level equivalent, if highlevel=False) with a new name.
ak.with_parameter	An array with a parameter set on the outermost node of its #ak.Array.layout.
ak.without_parameters	An array without any parameters in its #ak.Array.layout, on nodes of any level of depth.
ak.with_named_axis	An #ak.Array or #ak.Record (or low-level equivalent, if highlevel=False) with named axes attached.
ak.without_named_axis	An #ak.Array or #ak.Record (or low-level equivalent, if highlevel=False) without named axes.
ak.fields	A list of the field names (or tuple slot numbers) of the outermost record of array (many types supported, including all Awkward Arrays and Records).
ak.parameters	The parameters dict of the outermost node of array (many types supported, including all Awkward Arrays and Records).

[github-actions]

The documentation preview is ready to be viewed at http://preview.awkward-array.org.s3-website.us-east-1.amazonaws.com/PR4134