Docs/tutorial fixes

[sujandumaru]

Describe your changes

While reviewing the tutorials, I found several minor typos, malformed RST markup, and some code that could confuse readers. This PR fixes those tutorial issues and also updates the PGN Requests tutorial to match the current API.

• Clarifies create_internal_control_function preferred-address usage in the ISOBUS Hello World tutorial.
• Fixes minor tutorial typos and malformed RST markup.
• Updates the PGN Requests tutorial to use the current PGN request protocol API:
  • removes references to deleted protocol assignment/getter APIs
  • uses internalECU->get_pgn_request_protocol().lock()
  • fixes callback signatures and std::shared_ptr namespace usage
  • adds complete callback return paths in snippets
• Fixes the ESP32 PlatformIO link markup warning so the Sphinx build is warning-free.

Attempts to fix #514 at the same time.

How has this been tested?

Ran the documentation build locally after installing the Sphinx requirements and generating Doxygen XML.

python3 -m venv /docs-build
/docs-build/bin/pip install -r sphinx/requirements.txt

doxygen doxyfile

cd sphinx
/docs-build/bin/sphinx-build -M html source build -E -a