docs: Add examples and undocumented callback funcs

[CodeYan01]

Adds the following undocumented functions:

• calldata_set_data
• calldata_get_int
• calldata_get_float
• calldata_get_bool
• calldata_get_ptr
• calldata_get_string
• calldata_get_data

Description

Also adds details and examples on the following functions

Disclaimer: For the additional text under the Common Source Signals, Source-specific signals and procedures, and Core OBS Signals, I first wrote my own description for it, and had ChatGPT assistance for grammar and conciseness improvements, and manually reviewed its responses, not using them blindly.

Motivation and Context

Undocumented functions, and unclear how to use source signals and procs. Let's lower the barrier to entry for developers.

How Has This Been Tested?

Built the docs and viewed locally. Code examples aren't fully tested, but i wrote those first in an ide (for syntax highlighting and code completion, ensuring the functions exist) and having references in the obs source code that i merely adapted. I've also used these functions before so I know them.

Types of changes

• Documentation (a change to documentation pages)

Checklist:

• [x] My code has been run through clang-format.
• [x] I have read the contributing document.
• [x] My code is not on the master branch.
• [x] The code has been tested.
• [x] All commit messages are properly formatted and commits squashed where appropriate.
• [x] I have included updates to all appropriate documentation.

[CodeYan01]

Applied requested changes, thanks