Improve Falcon parser

Let me first say that it was a privilege to meet @sirosen @ EuroPython '26.
As I also replied on LinkedIn to @InessaPawson, the little BoF session on AI impact (that we participated in) was definitely one of the conference's main highlights for me.

IIRC I offered to help to improve Falcon "parser", but now that I've opened the code, it is not as trivial as I thought.

Main things that I'm unsure about (in progress):

• Do we want to DRY URL-encoded forms with Falcon's media handling? Do we need to keep the parse_form_body(...) helper for backwards compatibility, or is it considered private? Do we want to silence Unicode errors as it does?
• How to load media/request body in the async case? Is it properly supported for AIOHTTP?
• Add a recipe how to integrate this in middleware (in possible).

I will create a Draft PR addressing some of the mundane improvements, the rest needs discussion (since I don't have much experience with webargs).

Start by reading the Falcon parser code and the parse_form_body(...) helper. Review the open questions around URL-encoded forms, media handling, Unicode errors, async AIOHTTP request bodies, and middleware integration before choosing a focused scope. Done means the intended behavior and compatibility expectations are agreed and the selected improvements are covered.