mavlogdump: keep one-off and burst messages when using --reduce-rate

[azrabano23]

What was wrong

mavlogdump.py --reduce-rate N drops the parameter download from a tlog, even with --parms (issue #1033). On a synthetic tlog containing 100 ATTITUDE at 50 Hz, a burst of 10 PARAM_VALUE 5 ms apart, 5 STATUSTEXT 5 ms apart, and 1 Hz HEARTBEATs from two components 50 ms apart:

$ mavlogdump.py --reduce-rate 10 in.tlog --output out.tlog --quiet --parms
# message counts in out.tlog, master:
{'ATTITUDE': 17, 'HEARTBEAT': 1}

All 10 PARAM_VALUE and all 5 STATUSTEXT are gone, and one of the two heartbeat sources disappears entirely.

Root cause

reduce_rate_msg() exempts a fixed list of message types from rate reduction, but the list only contains DataFlash names (PARM, MSG, FMT, ...). Their tlog equivalents (PARAM_VALUE, STATUSTEXT) are rate-limited like any streaming message, so a burst is reduced to at most its first element. The --parms handling further down the loop is never reached because the message has already been discarded. The list also has EVT, which is not a DataFlash message; the event message is EV (as the --meta list in the same file already uses).

The fix

Extend the exempt list, following the discussion on the issue:

• PARAM_VALUE, STATUSTEXT: tlog equivalents of PARM, MSG; sent in bursts, not at a steady rate.
• MISSION_ITEM_INT, CMD: mission download, same reasoning.
• HEARTBEAT: sent at 1 Hz by every component; with two sources a few ms apart, rate limiting drops one source completely.
• EVT -> EV, plus ERR (one-off DataFlash messages, matching MAVExplorer's cmd_messages).

AUTOPILOT_VERSION was left out as agreed on the issue (sent once, so unaffected by rate limiting in practice).

After the change, on the same input:

{'ATTITUDE': 17, 'PARAM_VALUE': 10, 'STATUSTEXT': 5, 'HEARTBEAT': 4}

Verification

Added test_reduce_rate_keeps_oneoff_tlog_messages in tests/test_mavlogdump.py. It writes the synthetic tlog described above, runs mavlogdump.py --reduce-rate 10 --quiet --parms --output, reads the output back with mavutil.mavlink_connection, and asserts all PARAM_VALUE, STATUSTEXT and HEARTBEAT messages survive while ATTITUDE is reduced. It fails on master (assert 0 == 10 for PARAM_VALUE) and passes with this change.

python3 -m pip install .
python3 -m pytest tests/test_mavlogdump.py -q   # 2 passed
flake8 tools/mavlogdump.py tests/test_mavlogdump.py --count --select=E9,F63,F7,F82   # 0

Tested with Python 3.12 on macOS.

Fixes #1033

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