Make 'dist' preparation as lazy as possible

This avoid an explicit requirement (name @ url) from being prepared too
eagerly when its metadata is not required.

Co-authored-by: Richard Si <[email protected]>

Author: uranusjr

src/pip/_internal/resolution/resolvelib/candidates.py

@@ -1,3 +1,4 @@
+import functools
 import logging
 import sys
 from typing import TYPE_CHECKING, Any, FrozenSet, Iterable, Optional, Tuple, Union, cast
@@ -138,7 +139,6 @@ class exposes appropriate information to the resolver.
         found remote link (e.g. from pypi.org).
     """
 
-    dist: BaseDistribution
     is_installed = False
 
     def __init__(
@@ -156,7 +156,6 @@ def __init__(
         self._ireq = ireq
         self._name = name
         self._version = version
-        self.dist = self._prepare()
         self._hash: Optional[int] = None
 
     def __str__(self) -> str:
@@ -231,7 +230,8 @@ def _check_metadata_consistency(self, dist: BaseDistribution) -> None:
         except InvalidRequirement as e:
             raise MetadataInvalid(self._ireq, str(e))
 
-    def _prepare(self) -> BaseDistribution:
+    @functools.cached_property
+    def dist(self) -> BaseDistribution:
         try:
             dist = self._prepare_distribution()
         except HashError as e: