Check compatibility with Python 3.15 rc1

[gvanrossum]

3.15 is coming and the first release candidate is out today. we should at least check whether this is supported yet. (I expect typeagent itself to be fine, but we have some dependencies that may lag.)

[gvanrossum]

First problem is tiktoken, which doesn't compile. I filed openai/tiktoken#589

[gvanrossum]

To be able to build tiktoken from source you need the Rust compiler. I used

curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh

(I also updated the minimal tiktoken version to 0.13.0.)

The next hurdle is PyO3 -- I get this message (among many others):

        error: the configured Python version (3.15) is newer than PyO3's maximum supported version (3.14)
        = help: this package is being built with PyO3 version 0.27.2
        = help: check https://crates.io/crates/pyo3 for the latest PyO3 version available
        = help: updating this package to the latest version of PyO3 may provide compatibility with this Python version
        = help: set PYO3_USE_ABI3_FORWARD_COMPATIBILITY=1 to suppress this check and build anyway using the stable ABI

[gvanrossum]

Using export PYO3_USE_ABI3_FORWARD_COMPATIBILITY=1 (from the hint in that message) I got PyO3 to build, but now Pydantic-core doesn't build, so I'm giving up.

[gvanrossum]

Either uv or Pydantic did something (though I don't understand what) and now pydantic-core builds. But you still need that export for PyO3. I filed PyO3/pyo3#6293.

[gvanrossum]

Looks like everything now works -- there's a newer Pydantic version out that fixes the 3.15 issues, and the rest is addressed by installing rustc. I'm cleaning up pyproject.html and uv.lock next.