zbus: Add linker support, documentation and linum-stm32h753bi configuration

[JorgeGzm]

Summary

Integration of the zbus message bus port (apache/nuttx-apps#3743) on
top of the iterable sections infrastructure (#19927, merged), in two
commits (NuttX-side zbus support, then the board adoption):

1. zbus linker support: the zbus ITERABLE_SECTION() blocks,
   guarded by CONFIG_ZBUS, in include/nuttx/linker/common-rom.ld
   (include mode) and common-insert.ld (zero-touch INSERT mode of
   include/nuttx: Add link-time iterable sections infrastructure #19927); plus the zbus Sphinx documentation.
2. linum-stm32h753bi adoption (first adopter board): 2 #include
   lines in flash.ld and a zbus board configuration enabling the
   zbus example, its cmocka test suite and the OS test (ostest),
   reproducible with ./tools/configure.sh linum-stm32h753bi:zbus.

This resubmits the content of #19916, which was merged and then reverted
in #20009 because it landed before apache/nuttx-apps#3743: the board
configuration enables CONFIG_EXAMPLES_ZBUS and CONFIG_TESTING_ZBUS,
which only exist once the application side is in. Both dependencies are
declared with depends-on: lines, and this PR should only be merged
after both of them.

Impact

• Users: zbus becomes usable out of the box on the
  linum-stm32h753bi through the new :zbus configuration; any other
  board can adopt it the same way (two linker-script lines, or the
  INSERT mode with no board edit).
• Existing boards/configs: none. The included fragments expand to
  nothing unless CONFIG_ZBUS is enabled (verified: the stock :nsh
  map has zero zbus sections).
• Build process: no build logic touched in this PR (the INSERT-mode
  hook lives in include/nuttx: Add link-time iterable sections infrastructure #19927); Make and CMake both supported for the include
  mode.
• Hardware: only the linum-stm32h753bi board is touched.
• Documentation: zbus application pages and a zbus entry in the
  board configuration list.
• Tooling: the reused zbus SVG diagrams are added to the
  .codespellrc skip list (their embedded base64 raster data trips the
  spell checker with false positives).
• Security / compatibility: no changes to existing runtime code.

Testing

Host: Ubuntu 24.04.4 x86_64, arm-none-eabi-gcc 13.2.1 (GNU ld 2.41).
Target: linum-stm32h753bi (STM32H753BI), built with #19927 and
apache/nuttx-apps#3743 applied (as CI does).

• Stock :nsh build: no zbus references in the map or in the
  preprocessed linker script (no-op proof).

• :zbus build (Make and CMake): OK, the three _zbus_*_list sections
  collected name-sorted in flash as required by the zbus VDED algorithm.

• On hardware (ST-LINK V3): the 17-test zbus cmocka suite passes twice
  in the same boot and the zbus example produces the expected output,
  with the fourth message correctly masked for the listener and the
  listener notified before the subscriber:

  nsh> zbus
  zbus: publishing 5 messages to acc_chan
  zbus:  listener: x=1 y=10 z=100
  zbus:  subscriber: x=1 y=10 z=100
  zbus:  listener: x=2 y=20 z=200
  zbus:  subscriber: x=2 y=20 z=200
  zbus:  listener: x=3 y=30 z=300
  zbus: listener masked
  zbus:  subscriber: x=3 y=30 z=300
  zbus: listener unmasked
  zbus:  subscriber: x=4 y=40 z=400
  zbus:  listener: x=5 y=50 z=500
  zbus:  subscriber: x=5 y=50 z=500
  zbus: done
  

• ostest on the same boot, after the zbus suite (the zbus async
  listener task stays alive throughout): ostest_main: Exiting with status 0, no failures.

• INSERT mode: common-insert.ld preprocessed with CONFIG_ZBUS expands
  to the three zbus ITERABLE_SECTION blocks inside .iterable_sections
  (INSERT AFTER .text) and to an empty section without it;
  common-rom.ld expands to nothing in that mode.

• tools/checkpatch.sh -c -u -m -g on both commits (nxstyle +
  codespell, same flags as CI): all checks pass. sphinx-build -W:
  clean.

Depends-On #20015
Depends-On apache/nuttx-apps/pull/3743

[github-actions]

MemBrowse Memory Report

No memory changes detected for:

• arduino-mega2560
• esp32-devkitc
• hifive1-revb
• mirtoo
• qemu-armv8a
• qemu-intel64
• rx65n-rsk2mb
• s698pm-dkit
• stm32-nucleo-f103rb