Support free threaded Python versions like '3.13t' (#973)

* Support free threaded Python versions like '3.13t'

Python wheels, pyenv, and a number of other tools use 't' in the Python
version number to identify free threaded builds. For example, '3.13t',
'3.14.0a1', '3.14t-dev'.

This PR supports that syntax in `actions/setup-python`, strips the "t",
and adds "-freethreading" to the architecture to select the correct
Python version.

See #771

* Add free threading to advanced usage documentation

* Fix desugaring of `3.13.1t` and add test case.

* Add freethreaded input and fix handling of prerelease versions

* Fix lint

* Add 't' suffix to python-version output

* Use distinct cache key for free threaded Python

* Remove support for syntax like '3.14.0a1'

* Clarify use of 't' suffix

* Improve error message when trying to use free threaded Python versions before 3.13

docs/advanced-usage.md

@@ -77,6 +77,31 @@ steps:
 - run: python my_script.py
 ```
 
+You can specify the [free threading](https://docs.python.org/3/howto/free-threading-python.html) version of Python by setting the `freethreaded` input to `true` or by using the special **t** suffix in some cases.
+You can use the **t** suffix when specifying the major and minor version (e.g., `3.13t`), with a patch version (e.g., `3.13.1t`), or with the **x.y-dev syntax** (e.g., `3.14t-dev`).
+Free threaded Python is only available starting with the 3.13 release.
+
+```yaml
+steps:
+- uses: actions/checkout@v4
+- uses: actions/setup-python@v5
+  with:
+    python-version: '3.13t'
+- run: python my_script.py
+```
+
+Note that the **t** suffix is not `semver` syntax. If you wish to specify a range, you must use the `freethreaded` input instead of the `t` suffix.
+
+```yaml
+steps:
+- uses: actions/checkout@v4
+- uses: actions/setup-python@v5
+  with:
+    python-version: '>=3.13'
+    freethreaded: true
+- run: python my_script.py
+```
+
 You can also use several types of ranges that are specified in [semver](https://github.com/npm/node-semver#ranges), for instance:
 
 - **[ranges](https://github.com/npm/node-semver#ranges)** to download and set up the latest available version of Python satisfying a range: