test(discovery): fixtures for the parsers, the bounded sweep and the surfaces

tests/test_installed_apps.py is new and is where the discovery claims are
pinned. NO REAL SHIELD WAS AVAILABLE, so the command output is fixture-based
in the documented Android shapes — `pm list packages` lines, the verbose
`resolve-activity` header followed by `package/activity`, and `pm dump`
carrying `application-label` — including a localized label (the default
locale wins), a label-less app (a definitive negative, and still a row) and
the launcher (a system app that must be present).

Covered: both parsers plus their tolerances (noise, duplicates, blank,
a bare `package/activity` line, the settings entry point that is not a
launcher), the user+launcher merge and its de-duplication, the icon
heuristic and that it is always a string, the sweep's commands, its
concurrency bound (peak <= APP_SWEEP_CONCURRENCY and > 1, so it is bounded
AND genuinely concurrent), cache reuse with zero shells, the TTL, shared
sweeps for concurrent callers, and every degradation path (no poller,
disconnected, mute transport — empty list, no loop, no raise). The sensor's
count/table/reason and the "a failed refresh is a no-op, not an exception"
behaviour are pinned too.

The config-flow side is in tests/test_config_flow_ux.py: the table lists
every discovered app, a discovered app the map never mentions is appended,
the user's name wins for the same package, an `mdi:` value never reaches the
icon column, rendering issues no shell, the Discover row runs one forced
sweep and returns to the menu, a failed sweep still renders, and the merged
table round-trips into the saved options.

Also: tests/test_config_flow_real_ha.py learns the new row, the standalone
stub accepts `description_placeholders` (which the apps form now passes),
and the state=6 wording in media_session.py/media_player.py is the t57
UNIT 0c reword.

custom_components/nvidia_shield/ha_adb_common/media_session.py

@@ -20,9 +20,11 @@ class MediaSessionInfo:
 
     ``playing``/``paused``/``buffering`` are independent flags mapped from the
     Android PlaybackState integer: 2 = paused, 3 = playing, 6 = buffering
-    (t55). The Shield's own ExoPlayer/MediaSession sessions report state 6
-    while buffering just as stock Android does, so no vendor-specific state
-    integer is treated as buffering.
+    (t55). 6 is the stock-Android buffering value and the mapping is INFERRED
+    from the ``state=PlaybackState {state=N, ...}`` line shape, not from a
+    captured Shield dump: no fixture in this repo contains state=6, and no
+    real device was available. Nothing here is vendor-specific either way —
+    every integer is read straight out of the dump.
     """
 
     title: str | None = None