Drop Python 3.9 support (#301)

Contributes to rapidsai/build-planning#88

Finishes the work of dropping Python 3.9 support.

This project stopped building / testing against Python 3.9 as of rapidsai/shared-workflows#235.
This PR updates configuration and docs to reflect that.

## Notes for Reviewers

### How I tested this

Checked that there were no remaining uses like this:

```shell
git grep -E '3\.9'
git grep '39'
git grep 'py39'
```

And similar for variations on Python 3.8 (to catch things that were missed the last time this was done).

Authors:
  - James Lamb (https://github.com/jameslamb)

Approvers:
  - https://github.com/jakirkham

URL: #301

dependencies.yaml

@@ -396,10 +396,6 @@ dependencies:
     specific:
       - output_types: conda
         matrices:
-          - matrix:
-              py: "3.9"
-            packages:
-              - python=3.9
           - matrix:
               py: "3.10"
             packages:
@@ -410,7 +406,7 @@ dependencies:
               - python=3.11
           - matrix:
             packages:
-              - python>=3.9,<3.12
+              - python>=3.10,<3.12
   run_py_cuvs:
     common:
       - output_types: [conda, pyproject]

pyproject.toml

@@ -1,6 +1,6 @@
 [tool.black]
 line-length = 79
-target-version = ["py39"]
+target-version = ["py310"]
 include = '\.py?$'
 force-exclude = '''
 /(

python/cuvs/pyproject.toml

@@ -29,7 +29,7 @@ authors = [
     { name = "NVIDIA Corporation" },
 ]
 license = { text = "Apache 2.0" }
-requires-python = ">=3.9"
+requires-python = ">=3.10"
 dependencies = [
     "cuda-python",
     "numpy>=1.23,<2.0a0",
@@ -42,8 +42,8 @@ dependencies = [
 classifiers = [
     "Intended Audience :: Developers",
     "Programming Language :: Python",
-    "Programming Language :: Python :: 3.9",
     "Programming Language :: Python :: 3.10",
+    "Programming Language :: Python :: 3.11",
 ]
 
 [project.optional-dependencies]