Fix deep_sleep() opcode after the protocol 2.1 split (0x0052 -> 0x0053)

[sappafrancesco]

Fixes #159.

Protocol 2.1 split the old single 0x0052 opcode in two (per
opendisplay-protocol's opendisplay_protocol.h):

• CMD_POWER_OFF (0x0052) — a hard rail-cut for boards with a D-FF
  power latch; NACKs (OD_ERR_POWER_OFF_UNSUPPORTED) on latch-less
  boards.
• CMD_DEEP_SLEEP (0x0053) — host-commanded timer deep sleep, with an
  optional big-endian u16 one-shot wake-timer duration (60 s firmware
  floor). This is what deep_sleep() used to send on 0x0052.

deep_sleep() still sends 0x0052, so on current latch-less firmware
it now NACKs instead of sleeping — verified live on an M5Stack
PaperS3 (firmware protocol v2.2) per the issue.

Changes

• CommandCode.DEEP_SLEEP is now 0x0053; added
  CommandCode.POWER_OFF = 0x0052.
• build_deep_sleep_command() builds 0x0053 and takes an optional
  duration_seconds, appended as a big-endian u16 (not validated
  client-side against the firmware's 60 s floor, matching how other
  firmware-enforced limits are handled elsewhere in this library).
• Added build_power_off_command() (0x0052) and
  OpenDisplayDevice.power_off(), mirroring deep_sleep()'s existing
  tolerate-the-disconnect handling — a board with a power latch is
  expected to ACK 0x0052 and then drop the link exactly like
  deep_sleep()'s targets do, so the same ACK/NACK/timeout/disconnect
  logic applies.
• deep_sleep()'s NACK check moved from the 0xFF52 error frame to
  0xFF53 to match the new opcode.

Testing

tests/unit/test_device_deep_sleep.py renamed its 0x0052 assertions
to 0x0053, added a duration-parameter test, and added power_off()
coverage (ACK, NACK, write-drop, read-disconnect). Added
CommandCode.POWER_OFF/DEEP_SLEEP value assertions and
build_power_off_command()/duration-parameter coverage to
test_protocol_commands.py.

uv run pytest        -> 1035 passed
uv run ruff check     -> clean
uv run ruff format    -> clean
uv run mypy src/      -> clean (strict)
uv run pylint src/    -> 10.00/10

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

📢 Thoughts on this report? Let us know!