system/uorb: bump listener stack when float print extension is on

[FelipeMdeO]

Summary

uorb_listener's %pB debug printing (orb_info() -> lib_bsprintf()) performs real floating-point-to-string conversion synchronously, inside the listener's own task -- it is not a lightweight pointer dump. With CONFIG_LIBC_PRINT_EXTENSION off, %pB just prints a raw pointer and the default CONFIG_UORB_STACKSIZE (DEFAULT_TASK_STACKSIZE, 2048 on most configs) is plenty. With it on, decoding a topic's float fields through this path silently overflows a 2048-byte stack.

Confirmed on real hardware (ESP32-S3, two subscribed float topics pushing every ~10-20ms): uorb_listener hangs completely after printing only a partial topic name -- no panic, no stack dump, nothing -- because CONFIG_SCHED_STACKGUARD/CONFIG_STACK_COLORATION aren't on by default either, so there's no guard to catch the overflow before it corrupts adjacent memory.

Raising the default only when CONFIG_LIBC_PRINT_EXTENSION is set (not unconditionally, and not keyed off CONFIG_DEBUG_UORB specifically, since anything else that selects the same libc extension hits the same path) keeps the common case -- raw pointer output, small stack -- exactly as before, and only pays for the extra stack when the feature that needs it is actually enabled.

Impact

CONFIG_UORB_STACKSIZE default changes from DEFAULT_TASK_STACKSIZE to 4096 only for configs with CONFIG_LIBC_PRINT_EXTENSION=y. No change for any other config. Users who already have an explicit CONFIG_UORB_STACKSIZE recorded in their .config are unaffected by this default either way (see note below).

Testing

Host: Ubuntu 24.04.4 LTS. xtensa-esp-elf-gcc (crosstool-NG esp-14.2.0_20241119) 14.2.0. checkpatch.sh (style + -m commit message) clean.

On hardware -- Seeed XIAO ESP32-S3, CONFIG_LIBC_PRINT_EXTENSION=y, uorb_listener subscribed to two float-based topics streaming continuously:

• CONFIG_UORB_STACKSIZE=2048 (the old default): reproduces the hang every time, output cuts off mid topic-name print, console never responds again.

• CONFIG_UORB_STACKSIZE=4096 (this PR's new default): runs cleanly, verified repeatedly across multiple fresh boots for 10+ seconds continuous, fully decoded output, e.g.:

  sensor_gyro(now:20410000):timestamp:20410000,x:0.008399,y:-0.041386,z:0.017409,temperature:31.000000
  sensor_accel(now:20390000):timestamp:20390000,x:-6.385280,y:0.358925,z:-7.318485,temperature:31.000000
  

• End-to-end with the actual Kconfig default mechanism (not a manual override): starting from a .config where CONFIG_UORB_STACKSIZE was never set, enabling CONFIG_LIBC_PRINT_EXTENSION and running make olddefconfig resolves CONFIG_UORB_STACKSIZE to 4096 automatically; the resulting build was flashed and validated live on the bench with the same clean, continuous decoded output as above.