Allow callable functions to be passed directly into hx_* attributes

[AaineeSinha]

Solves #864

Summary of the Issue & Changes

1. What the Problem Was

When passing router-decorated callable functions directly into hx_* attributes (like hx_post, hx_get, etc.), FastHTML did not automatically resolve them to their string URL paths. Developers were forced to explicitly wrap every function in str(), creating unnecessary friction, type-annotation mismatches, and messy code when attempting to use reverse routing.

2. What I Changed (The Solution)

I implemented automatic string resolution for callables passed into HTMX attributes to enable clean, native reverse routing.

• Core Attribute Logic (fasthtml/components.py): Modified the component rendering logic to intercept callables in hx_* proxy attributes and automatically convert them to their corresponding string paths internally.
• Documentation & Notebooks (nbs/api/01_components.ipynb): Updated the source notebook to formally support this behavior, adjusted the component documentation examples, and added structural verification tests to ensure decorated functions resolve perfectly without manual casting.