Support granular target Python versions (#534)

## Summary

Allows, e.g., `--python-version 3.7` or `--python-version 3.7.9`. This
was also feedback I received in the original PR.

Closes https://github.com/astral-sh/puffin/issues/533.

crates/puffin-cli/tests/pip_compile.rs

@@ -473,7 +473,7 @@ fn compile_python_312() -> Result<()> {
             .arg("pip-compile")
             .arg("requirements.in")
             .arg("--python-version")
-            .arg("py312")
+            .arg("3.12")
             .arg("--cache-dir")
             .arg(cache_dir.path())
             .arg("--exclude-newer")
@@ -502,7 +502,7 @@ fn compile_python_37() -> Result<()> {
             .arg("pip-compile")
             .arg("requirements.in")
             .arg("--python-version")
-            .arg("py37")
+            .arg("3.7")
             .arg("--cache-dir")
             .arg(cache_dir.path())
             .arg("--exclude-newer")
@@ -514,6 +514,50 @@ fn compile_python_37() -> Result<()> {
     Ok(())
 }
 
+/// Resolve a specific version of Black against an invalid Python version.
+#[test]
+fn compile_python_invalid_version() -> Result<()> {
+    let temp_dir = TempDir::new()?;
+
+    let requirements_in = temp_dir.child("requirements.in");
+    requirements_in.write_str("black==23.10.1")?;
+
+    insta::with_settings!({
+        filters => INSTA_FILTERS.to_vec()
+    }, {
+        assert_cmd_snapshot!(Command::new(get_cargo_bin(BIN_NAME))
+            .arg("pip-compile")
+            .arg("requirements.in")
+            .arg("--python-version")
+            .arg("3.7.x")
+            .current_dir(&temp_dir));
+    });
+
+    Ok(())
+}
+
+/// Resolve a specific version of Black against an invalid Python version.
+#[test]
+fn compile_python_dev_version() -> Result<()> {
+    let temp_dir = TempDir::new()?;
+
+    let requirements_in = temp_dir.child("requirements.in");
+    requirements_in.write_str("black==23.10.1")?;
+
+    insta::with_settings!({
+        filters => INSTA_FILTERS.to_vec()
+    }, {
+        assert_cmd_snapshot!(Command::new(get_cargo_bin(BIN_NAME))
+            .arg("pip-compile")
+            .arg("requirements.in")
+            .arg("--python-version")
+            .arg("3.7-dev")
+            .current_dir(&temp_dir));
+    });
+
+    Ok(())
+}
+
 /// Test that we select the last 3.8 compatible numpy version instead of trying to compile an
 /// incompatible sdist <https://github.com/astral-sh/puffin/issues/388>
 #[test]

crates/puffin-cli/tests/snapshots/pip_compile__compile_python_312.snap

@@ -6,17 +6,19 @@ info:
     - pip-compile
     - requirements.in
     - "--python-version"
-    - py312
+    - "3.12"
     - "--cache-dir"
-    - /tmp/.tmp4asOTQ
+    - /var/folders/nt/6gf2v7_s3k13zq_t3944rwz40000gn/T/.tmpBGkaCR
+    - "--exclude-newer"
+    - "2023-11-18T12:00:00Z"
   env:
-    VIRTUAL_ENV: /tmp/.tmpjRCdtR/.venv
+    VIRTUAL_ENV: /var/folders/nt/6gf2v7_s3k13zq_t3944rwz40000gn/T/.tmpfxl60Y/.venv
 ---
 success: true
 exit_code: 0
 ----- stdout -----
 # This file was autogenerated by Puffin v0.0.1 via the following command:
-#    puffin pip-compile requirements.in --python-version py312 --cache-dir [CACHE_DIR]
+#    puffin pip-compile requirements.in --python-version 3.12 --cache-dir [CACHE_DIR]
 black==23.10.1
 click==8.1.7
     # via black

crates/puffin-cli/tests/snapshots/pip_compile__compile_python_dev_version.snap

@@ -0,0 +1,19 @@
+---
+source: crates/puffin-cli/tests/pip_compile.rs
+info:
+  program: puffin
+  args:
+    - pip-compile
+    - requirements.in
+    - "--python-version"
+    - 3.7-dev
+---
+success: false
+exit_code: 2
+----- stdout -----
+
+----- stderr -----
+error: invalid value '3.7-dev' for '--python-version <PYTHON_VERSION>': Python version 3.7-dev is a development release
+
+For more information, try '--help'.
+

crates/puffin-cli/tests/snapshots/pip_compile__compile_python_invalid_version.snap

@@ -0,0 +1,19 @@
+---
+source: crates/puffin-cli/tests/pip_compile.rs
+info:
+  program: puffin
+  args:
+    - pip-compile
+    - requirements.in
+    - "--python-version"
+    - 3.7.x
+---
+success: false
+exit_code: 2
+----- stdout -----
+
+----- stderr -----
+error: invalid value '3.7.x' for '--python-version <PYTHON_VERSION>': Version `3.7.x` doesn't match PEP 440 rules
+
+For more information, try '--help'.
+