SITL: extend SerialDevice corruption simulation

[tatsuy]

This change extends the SITL SerialDevice corruption simulator to cover more UART/serial failure modes, making it easier to stress-test serial parsers under Valgrind and catch potential buffer overruns.

What’s added

• stall: return 0 bytes even though data was available
• short-read: return only a short prefix of the available bytes
• burst: corrupt a small consecutive range of bytes

drop/add/flip are kept as-is.

Notes

• This is guarded behind AP_SIM_SERIALDEVICE_CORRUPTION_ENABLED, so there is no behavior change when corruption is disabled.
• Intended usage is to enable corruption and run SITL under Valgrind (e.g. sim_vehicle.py -V) to verify there are no memory errors even under heavy serial corruption.

[peterbarker]

This looks OK, but we're now corrupting a lot of bytes!

How was this tested?

[tatsuy]

I used this commit to test the serial-corruption scenarios for #31663 in SITL under Valgrind. The corruption scenarios were useful because they exposed an additional packet-boundary handling issue, and I was able to add a fix for it.

I didn’t add per-mode unit tests (e.g. forcing each corruption type or packet dumps).