Click CLI type-checks under mypy strict without `# type: ignore[misc]`

Summary

Remove the blanket # type: ignore[misc] comments scattered across the Click CLI surface, replacing each with a properly typed construct so mypy --strict passes without suppression.

Motivation

There are 19 # type: ignore[misc] sites: 17 on the @click.command() / @click.option(...) / @click.argument(...) decorators in cli/main.py, one on EnumChoice(click.Choice) in cli/click.py, and one on ZFSReplicateError(ClickException) in error.py. They predate Click shipping inline type information (py.typed); the lockfile now resolves Click 8.1.8 (8.4+ in a fresh env), which is fully typed.

A quick check stripping the ignores from those three files and re-running mypy left only one real error — error.py:8: Class cannot subclass "ClickException" (has type "Any") [misc] — which suggests most of the decorator/Choice ignores are already stale and removable, while the ClickException subclass still needs a typed path. They mask whatever future signature mistakes mypy would otherwise catch on these decorators.

Surfaced while adding the receive-side flags in #393 / #455, where each new @click.option had to carry another copy of the ignore.

Scope

• Audit the 19 # type: ignore[misc] sites in cli/main.py, cli/click.py, and error.py.
• Drop the ones mypy no longer needs now that Click is typed.
• For any genuine remaining gap (e.g. subclassing ClickException), find a typed resolution — a typed shim, a narrower per-line ignore code, or a documented minimal suppression — rather than the broad [misc].

Acceptance criteria

• mypy --strict (the repo's mypy.ini) passes on zfs/ with no # type: ignore[misc] in cli/main.py, cli/click.py, or error.py.
• Any unavoidable suppression that remains uses a specific error code and a one-line comment explaining why, not a bare [misc].
• No new # type: ignore is introduced elsewhere to compensate.

Additional context

Overlaps #398 (drop Python 3.8/3.9 for v5.0.0), whose acceptance criteria include re-evaluating these same # type: ignore[misc] markers. This issue does that re-eval standalone, independent of the version-matrix change, so it can land first — closing it satisfies that slice of #398 early. Implemented by #458.