docs: Document `Attributes` for NamedTuple and dataclass fields

[tony]

autodoc renders every field of a NamedTuple, dataclass, or TypedDict whether or not the docstring describes it. An undocumented NamedTuple field reaches the API docs as "Alias for field number 0"; a dataclass or TypedDict field reaches it bare. AGENTS.md now requires an Attributes section covering every field, and this issue tracks the code that predates that rule.

14 classes are missing an Attributes entry for 74 fields in total.

Rendered on the published site today

These modules are named by an autodoc directive under docs/, so the stubs are live in the API docs right now.

• SubprocessCommand (dataclass) in libvcs._internal.subprocess — missing args, bufsize, executable, stdin, stdout, stderr, preexec_fn, close_fds, shell, cwd, env, creationflags, +13 more
• SyncError (dataclass) in libvcs.sync.base — missing step, message, exception
• SyncResult (dataclass) in libvcs.sync.base — missing ok, errors
• VCSLocation (NamedTuple) in libvcs.sync.base — missing url, rev
• GitRemote (dataclass) in libvcs.sync.git — missing name, fetch_url, push_url
• GitStatus (dataclass) in libvcs.sync.git — missing branch_oid, branch_head, branch_upstream, branch_ab, branch_ahead, branch_behind
• Rule (dataclass) in libvcs.url.base — missing weight
• GitBaseURL (dataclass) in libvcs.url.git — missing url, scheme, user, hostname, port, path, suffix, rule
• GitAWSCodeCommitURL (dataclass) in libvcs.url.git — missing region, rev
• GitPipURL (dataclass) in libvcs.url.git — missing rev
• HgBaseURL (dataclass) in libvcs.url.hg — missing url, scheme, user, hostname, port, separator, path, suffix, ref, rule
• HgPipURL (dataclass) in libvcs.url.hg — missing rev
• SvnBaseURL (dataclass) in libvcs.url.svn — missing url, scheme, user, hostname, port, separator, path, ref, rule
• SvnPipURL (dataclass) in libvcs.url.svn — missing rev

Fixing one

Add a NumPy-style Attributes section naming every field, with its type and what it holds:

class Example(t.NamedTuple):
    """One-line summary.

    Attributes
    ----------
    path : pathlib.Path | None
        What this field holds, and what ``None`` means.
    """

Partial coverage does not help: a class with three fields and two documented still ships a stub for the third.

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Links are permalinks anchored to v0.45.1; a file that changed since the last release is linked at the current trunk commit instead. Produced by a static AST scan of the package for NamedTuple, dataclass, and TypedDict classes whose docstring omits a field, excluding tests and private classes.