add setter for version on ProjectPackage

This enables support for dynamically setting the package version
(e.g., from a plugin)

Resolves: python-poetry/poetry#5493

src/poetry/core/packages/package.py

@@ -79,12 +79,7 @@ def __init__(
             features=features,
         )
 
-        if not isinstance(version, Version):
-            self._version = Version.parse(version)
-            self._pretty_version = pretty_version or version
-        else:
-            self._version = version
-            self._pretty_version = pretty_version or self._version.text
+        self._set_version(version, pretty_version)
 
         self.description = ""
 
@@ -216,6 +211,18 @@ def all_requires(
             for dependency in group.dependencies
         ]
 
+    def _set_version(self,
+                     version: str | Version,
+                     pretty_version: str | None = None) -> None:
+
+        if not isinstance(version, Version):
+            self._version = Version.parse(version)
+            self._pretty_version = pretty_version or version
+        else:
+            self._version = version
+            self._pretty_version = pretty_version or self._version.text
+
+
     def _get_author(self) -> dict[str, str | None]:
         if not self._authors:
             return {"name": None, "email": None}

src/poetry/core/packages/project_package.py

@@ -63,6 +63,10 @@ def python_versions(self, value: str) -> None:
             create_nested_marker("python_version", self._python_constraint)
         )
 
+    @version.setter
+    def version(self, value: str | Version) -> None:
+        self._set_version(value)
+
     @property
     def urls(self) -> dict[str, str]:
         urls = super().urls