llm-tool-collection-deftool: declare indent, doc-string and support for async tool

[kiennq]

Properly declare the indent and doc-string index for llm-tool-collection-deftool
Remove some autoload tag and font lock since it will be handled correctly after the llm-tool-collections is loaded.
And finally add support for async tool, where the body can take and callback-fn to notify the result back in async way to LLM

[skissue]

Thanks! I'm not too familiar with the font-lock and Imenu stuff. @ultronozm, would you mind taking a glance at this?

[ultronozm]

Looks fine to me except for the font-lock removal - I think I added that, and I seem to recall one of the points being to make fontification work well even before the package is loaded (e.g., on startup). So perhaps @kiennq could add some further motivation for that

[ultronozm]

I'm also curious about the #autoload deletions, which I thought were likewise included to make everything work well on start-up, possibly before the package itself is loaded

[skissue]

Hmm, I'm going to go ahead and merge the other changes for now. I would like to have support for async tools, I think some of the current tools are better suited to being async.