fix(providers/uv): treat uv.lock as optional

Closes #1383.

`UvProvider.set_lock_version()` unconditionally read `uv.lock`, which
made `cz bump` crash with `FileNotFoundError` whenever the lock had not
been written yet. The two reproducers in #1383 are:

- a freshly initialised uv project (`uv init`) before `uv sync` has run,
- a uv workspace member where the lock lives at the workspace root, not
  alongside the package's own `pyproject.toml`.

Add an `if not self.lock_file.exists(): return` early-out so updating
`pyproject.toml` is enough; the lock is rewritten only when present.

A regression test creates a `pyproject.toml` without a sibling `uv.lock`
and asserts that `set_version` updates the project file and does not
write a lock.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: bearomorphism

commitizen/providers/uv_provider.py

@@ -26,6 +26,12 @@ def set_version(self, version: str) -> None:
         self.set_lock_version(version)
 
     def set_lock_version(self, version: str) -> None:
+        if not self.lock_file.exists():
+            # `uv.lock` is optional: a freshly initialised project (or a uv
+            # workspace member, since the lock lives at the workspace root)
+            # may not have one yet. Updating `pyproject.toml` is enough.
+            return
+
         pyproject_toml_content = tomlkit.parse(
             self.file.read_text(encoding=self._get_encoding())
         )

tests/providers/test_uv_provider.py

@@ -119,3 +119,24 @@ def test_uv_provider(
 
     file_regression.check(updated_pyproject_toml_content, extension=".toml")
     file_regression.check(updated_uv_lock_content, extension=".lock")
+
+
+def test_uv_provider_without_lock_file(config: BaseConfig, tmp_path, monkeypatch):
+    """Regression for #1383: a freshly initialised uv project (or a uv
+    workspace member) has no `uv.lock` yet; bumping must still update
+    `pyproject.toml` instead of raising `FileNotFoundError`."""
+    monkeypatch.chdir(tmp_path)
+    pyproject_toml_file = tmp_path / UvProvider.filename
+    pyproject_toml_file.write_text(PYPROJECT_TOML, encoding="utf-8")
+    assert not (tmp_path / UvProvider.lock_filename).exists()
+
+    config.settings["version_provider"] = "uv"
+
+    provider = get_provider(config)
+    assert isinstance(provider, UvProvider)
+    assert provider.get_version() == "4.2.1"
+
+    provider.set_version("100.100.100")
+    assert provider.get_version() == "100.100.100"
+    assert "100.100.100" in pyproject_toml_file.read_text(encoding="utf-8")
+    assert not (tmp_path / UvProvider.lock_filename).exists()