FYI - python-build-standalone now builds dynamic Tkinter/Tcl/Tk

Hi! In today's release (20250808) of python-build-standalone we've split out `_tkinter`, `libtcl`, and `libtk` into their own dynamic libraries (astral-sh/python-build-standalone#676). This should address issues like #2540 where tkinter didn't work right. I'm opening this mostly because we're now generating three new .so files and I don't know if you need to adjust something on your end to pick them up. But also, if you see any issues with the new setup, please let me know, either here or by opening an issue in python-build-standalone.

Details on the implementation, if it's helpful:
* `_tkinter` is now a separate extension module and no longer statically linked into bin/python and libpython (so any user code using `_tkinter` will need to bundle the dynamic library and unpack it at runtime)
* There are separate `libtcl8.6.so` and `libtk8.6.so` (or `.dylib`) libraries inside our `lib` directory.
* On Linux, `bin/python3` has a `DT_RPATH` pointing it at the `lib` directory, so `import _tkinter` finds our copies of libtcl and libtk. Users of `libpython3.x.so` will need to set up rpaths or something on their own. (If it's helpful can add an rpath to `libpython3.x.so`, or tweak the `DT_NEEDED` in `_tkinter` to use `$ORIGIN/../../libtcl8.6.so` etc. (though that trick would only work for gllibc, not musl).
* On macOS, `lib/python3.x/lib-dynload/_tkinter.cpython-3x-darwin.so` has an `LC_RPATH` pointing at `@loader_path/../../`, and the install name of libtcl and the `LC_LOAD_DYLIB` entry in `_tkinter` is `@rpath/libtcl8.6.so.dylib`, and the same for libtk. So if you maintain the `lib/` directory structure you shouldn't need to fiddle with library paths on your own.
* libX11 and friends are now statically linked into `libtk` on Linux. At some point I might make these dynamic libraries and/or attempt to look for the system version.

Also, speaking of changes to dynamic libraries, as of a few months ago, our Linux builds statically link libpython into the interpreter, so you no longer need lib/libpython3.x.so.1 to run bin/python. We still ship libpython for the sake of people embedding Python into a larger program. At some point I want to split this out but I haven't yet figured out how to coordinate that transition.

Start by inspecting how rules_python consumes the python-build-standalone layout, especially bin/python3, lib/python3.x/lib-dynload/_tkinter.cpython-3x-darwin.so, and the lib directory. Verify whether the new _tkinter, libtcl8.6, and libtk8.6 dynamic libraries are included and whether both Python execution and libpython embedding remain functional.

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