[jihtsan]

Fixes #279.

Custom reStructuredText fields such as :calls: are not in the Sphinx field-name list, so wrapping can move their continuation lines to the field's own indentation and break the field/link structure.

Recognize extensible reST field markers at the start of a line, using the field-marker grammar rather than adding a calls exception. Keep the existing permissive Sphinx recognition for compatibility. Use only the marker span when wrapping, and keep a separating space before inline-link bodies as required by reST. Update the corresponding requirements-table entry; empty bodies still receive no trailing space.

Leave the existing list/code classifier unchanged so custom fields with complex bodies retain their previous protection. Add 24 cases covering custom/typed/Unicode/escaped-colon markers, prose and roles, long-link continuation indentation and idempotence, and module-level bullet/enumerated/doctest bodies.

Validation on macOS arm64:

• Against unchanged base: 12 new cases fail; 12 controls pass. With the fix all pass.
• Python 3.10.21: full suite 664 passed, 4 skipped.
• Python 3.14.6: full suite 665 passed, 3 skipped.
• Real CLI plus Docutils: original Issue function docstring retains all three fields and the exact URI, without warnings. Ten independent CLI/Docutils comparisons preserve complex field-body structures, fields, URIs and idempotence.
• Black 26.3.1, Ruff, isort, mypy, pydocstyle, source docformatter check and git diff check pass for the changed files/source as applicable.

Sphinx 6.2.1 (locked version) generates HTML on both base and branch, but strict -W builds both fail on the existing missing _static directory warning. That unrelated configuration is unchanged. Linux, Windows and other Python versions were not run locally. --force-wrap retains its documented flattening behavior. An independent module-level long-URI case has the same existing limitation on base and branch; this patch does not claim to repair that separate path.