[emrenorm]

Title: nrf91: fix "wait for events timed out" in modem firmware update; split commander lines once

Problem

On an nRF9151 with a CMSIS-DAP probe (DAPLink), nrf91-update-modem-fw
failed with wait for events timed out although the modem DFU itself works
(ModemUpdater.verify() from the Python API passes every time from a clean
state). Three independent causes all ended in the same misleading message:

1. The commander split command lines twice. _split_commands() splits
   into words (removing quotes/escapes), then parse_command() split the words
   again. Nordic's DECT NR+ package is named mfw-nr+_nrf91x1_1.0.1.zip; the
   path reached the command as three words, and neither quoting nor \+ helped.
2. Verify errors were swallowed. except: turned any verify error (here:
   FileNotFoundError) into a programming attempt. The verify had already left
   the modem in its DFU bootloader, so the second attempt timed out.
3. A second DFU with debug power still requested gets no answer. This hits
   the command's own verify-then-program path (same session) and any pyocd cmd
   run after another one, because the commander keeps the debug port powered on
   exit (resume_on_disconnect=False).

Changes

• commands: split command lines into words only once + unit test
  (test/unit/test_execution_context.py; fails on the old code for the quoted
  and escaped cases).
• nrf91: fix modem firmware update failures:
  • power-cycle the debug domain at the start of _setup_device();
  • only checksum mismatch / Error while verifying lead to programming,
    other errors propagate; parse() reports a missing file (hinting at quoting);
  • reset the device when verify/program ends, also after errors, so the modem
    leaves its DFU bootloader.

Testing (nRF9151 LACA A1A, ARM DAPLink on NUCLEO-F103RB, mfw-nr+_nrf91x1_1.0.1.zip)

Each line is a separate pyocd cmd -t nrf91 -c "nrf91-update-modem-fw ..." run:

Case	Before	After
unquoted path with +	timeout after 31 s	modem firmware file not found: _nrf91x1_1.0.1.zip (quote paths ...)
quoted path, verify, 4 consecutive runs	timeout	4/4 pass (~6 s)
package with altered digest (mismatch -> program, same session)	timeout	programs, then reports checksum mismatch
-f program + verify	—	pass (17 s), following verify passes

Measured but not changed: the IPC receive masks. Another tool uses 0xFFFF
for nRF9151; with the existing nRF9160 values (0x4/0x10) all cases above
pass, the modem signalled on channels 2 and 4.

Developed with assistance from Claude (Anthropic); I reviewed the changes and ran all tests on specific hardware.