tokens: speed up duplication of Tokens objects (#5325)

CHANGES.md

@@ -20,6 +20,13 @@ ones in. -->
 [#5314](https://github.com/cylc/cylc-flow/pull/5314) - Fix broken
 command option: `cylc vip --run-name`.
 
+[#5319](https://github.com/cylc/cylc-flow/pull/5319),
+[#5321](https://github.com/cylc/cylc-flow/pull/5321),
+[#5325](https://github.com/cylc/cylc-flow/pull/5325) -
+Various efficiency optimisations to the scheduler which particularly impact
+workflows with many-to-many dependencies (e.g. `<a> => <b>`).
+
+-------------------------------------------------------------------------------
 ## __cylc-8.1.0 (<span actions:bind='release-date'>Released 2023-01-16</span>)__
 
 ### Breaking Changes

cylc/flow/id.py

@@ -107,7 +107,10 @@ def __init__(
         if args:
             if len(args) > 1:
                 raise ValueError()
-            kwargs = tokenise(str(args[0]), relative)
+            if isinstance(args[0], str):
+                kwargs = tokenise(args[0], relative)
+            else:
+                kwargs = dict(args[0])
         else:
             for key in kwargs:
                 if key not in self._KEYS:

tests/integration/test_reinstall.py

@@ -80,7 +80,7 @@ def one_run(one_src, test_dir, run_dir):
     )
     return SimpleNamespace(
         path=w_run_dir,
-        id=w_run_dir.relative_to(run_dir),
+        id=str(w_run_dir.relative_to(run_dir)),
     )