MAINT-21: tests read and patch the Controller through tools/main_files.py

Prepares the split of app/main.py's Controller into files by job, with no app
change. tools/main_files.py gives a test the text and the AST of main.py plus
the files split from it, and `live`, which sets a global in every file whose
functions read it (and raises when none does). Tests that read main.py's
source, and tests and replay tools that patch a main global (datetime,
compute, resolve, _mono, WRITE_BUDGET_S, ...), go through it, so they pass on
this layout and on the split one. test_split_patches.py fails when a test or
tool patches an app.main attribute that main.py no longer reads, or that
another file also reads. tools/maint21_same_ast.py proves every function,
method and module-level assignment of main.py at the base is found unchanged
in its new file.

Co-Authored-By: Claude <noreply@anthropic.com>

goodwe_controller/test_peak_margin.py

@@ -22,6 +22,7 @@ import sys
 
 HERE = os.path.dirname(os.path.abspath(__file__))
 sys.path.insert(0, os.path.join(HERE, "tools"))
+import main_files  # noqa: E402
 
 import safety79_identity as rig                               # noqa: E402
 from named_absence import nth, present                        # noqa: E402
@@ -207,9 +208,8 @@ check("...and the user-facing peak notice built from the decision's limit "
 
 # ============================================================================ #
 print("\n4. each call site in main.py")
-with open(os.path.join(HERE, "app", "main.py"), encoding="utf-8") as f:
-    _src = f.read()
-_tree = ast.parse(_src)
+_src = main_files.source()
+_tree = main_files.tree(_src)
 
 
 def calls(name):