Better workspace/crates handling

[pepperoni21]

Hey, just published version 0.2.3 that introduces a macro crate for handling custom user-defined functions.

I'm not really used to publishing workspaces to crates.io. I just published both ollama-rs and ollama-rs-macros crates separately, and it requires ollama-rs to use the published version of ollama-rs-macros on crates.io so I specified the current version of the macro crate inside the Cargo.toml of ollama-rs:

ollama-rs-macros = { version = "0.2.3", optional = true }

While on the master branch it uses the workspace dependency. I don't know if there's a better way to handle that. Probably. Hopefully it doesn't break anything, and the master branch remains accessible for use as a dependency.