🐛 filter walk-in / non-web-bookable campsites by default (UseDirect)

[luckyrandom]

The bug

The UseDirect API (ReserveCalifornia and siblings) marks walk-in /
non-web-bookable nights as availability_status="Available", the same
status reservable sites get. Camply forwards every "Available" night to
the user, so cancellation watchers fire false-positive notifications on
sites that physically cannot be reserved online — the user races to
ReserveCalifornia.com, picks the date, and the site isn't even listed.

Concrete reproducer at Sugarloaf Ridge SP (campground id 731) for
2026-06-06:

camply campsites --provider ReserveCalifornia --campground 731 \
  --start-date 2026-06-06 --end-date 2026-06-07 --nights 1

Reports 3 "available" sites: #4, #5, #35. None of the three can
actually be booked via the website. Raw API dump for those same units:

site  AllowWebBooking  IsWalkin
#04   True             True
#05   False            True
#35   False            True

The data is already there in UseDirectAvailabilityUnit.AllowWebBooking
(per-site) and UseDirectAvailabilitySlice.IsWalkin (per-night). Camply
just wasn't reading them when deciding whether to surface a site.

Note that AllowWebBooking=True does not imply bookable — site #4 is
normally bookable but held back for walk-ups on this specific date,
which is what IsWalkin captures. Both flags must be checked.

The fix

Treat a slice as bookable only when:

availability_slice.IsWalkin is not True
and unit.AllowWebBooking is not False

The check is in the same loop in UseDirectProvider.get_campsites
that already filters by availability_status == "Available" — minimal
surface area, no new API calls.

Escape hatch

Add --include-walkin (off by default) so anyone who wants the old
behavior — or who's specifically hunting walk-ins — can opt back in:

camply campsites ... --include-walkin

Plumbing follows the existing --equipment pattern: click option in
cli.py, threaded through _get_provider_kwargs_from_cli into
provider_kwargs, accepted by SearchUseDirect.__init__, forwarded to
UseDirectProvider.get_campsites.

Verification

Same query as the reproducer above:

(default)              0 Reservable Campsites Matching   ✓
--include-walkin       3 Reservable Campsites Matching   ✓

Other providers (Recreation.gov, GoingToCamp, Yellowstone, …) are
unaffected — the param is UseDirect-specific and only the UseDirect
search class reads it.

Co-Authored-By: Claude Opus 4.7 noreply@anthropic.com

[luckyrandom]

Please let me know if it should be off by default for better backward compatibility.