fix: Ollama provider handling of canonical URLs

[vrurg]

Make the provider not only play well with canonical URLs but also implement the ground for safer URL management in the future.

Fixes #655.

[vrurg]

I have accidentally spotted a fix for the same problem in the openai provider. But I believe the approach proposed here is cleaner because it would intercept badly formed URLs while the agent is being built, not when an HTTP request gets submitted. This would significantly reduce debugging times in particular for both RIG users and developers because accidentally malformed post paths would also be nailed down early and clearly.

[vrurg]

Unfortunately, I cannot extend this PR to other providers due to lack of time. It looks like it can be copy/pasted into the openai code though.

[joshua-mo-143]

What version of Rust are you using? You might need to update to get the fmt test to pass

[joshua-mo-143]

lgtm once it passes CI

[vrurg]

It would be great to have a .rustfmt.toml in the root of the project. I accidentally left my own fmt config in ~/src/rust where I keep all Rust-related projects and this is what caused problems with formatting. Having local project config would prevent such accidents in the future.

Anyway, must be OK now.