test: enable async on RepoCase tests using start_enactment

Forward `$callers` from the calling process into the spawned Enactment
GenServer so Ecto's sandbox ownership lookup can find the test's
connection. This unblocks `async: true` for the 11 test files that
exercise a real Enactment via `start_enactment/2`. Also call
`Sandbox.allow/3` in the helper as belt-and-suspenders for any future
descendant processes.

The `$callers` pattern is the documented Elixir 1.17+ approach for
GenServers spawned from test processes. In production the chain is empty
and the change is a no-op.

`lifespan_test.exs` and `default_logger_test.exs` remain synchronous
because they mutate Application env / Logger config / telemetry handlers
keyed by stable handler ids. Snapshot-debounce telemetry handler in
`enactment_test.exs` is narrowed to filter by `metadata.enactment_id` so
concurrent enactments don't pollute its burst measurement.

Wall-clock test time drops ~30-45% on the local machine.

Author: fahchen

lib/coloured_flow/runner/enactment/enactment.ex

@@ -96,6 +96,10 @@ defmodule ColouredFlow.Runner.Enactment do
   @spec start_link(options()) :: GenServer.on_start()
   def start_link(options) do
     enactment_id = Keyword.fetch!(options, :enactment_id)
+    # Forward `$callers` from the calling process so collaborating processes
+    # (e.g., Ecto.Adapters.SQL.Sandbox-aware tests) can be tracked. See
+    # `ExUnit.Callbacks.start_supervised/2` for the recommended pattern.
+    options = Keyword.put_new(options, :"$callers", Process.get(:"$callers", []))
 
     GenServer.start_link(
       __MODULE__,
@@ -107,10 +111,13 @@ defmodule ColouredFlow.Runner.Enactment do
 
   @impl GenServer
   def init(options) do
-    state =
-      __MODULE__
-      |> struct(options)
-      |> Map.put(:hibernate_after, Lifespan.hibernate_after_from_options(options))
+    {callers, options} = Keyword.pop(options, :"$callers", [])
+    Process.put(:"$callers", callers)
+
+    options =
+      Keyword.put(options, :hibernate_after, Lifespan.hibernate_after_from_options(options))
+
+    state = struct(__MODULE__, options)
 
     {:ok, state, {:continue, :populate_state}}
   end

test/coloured_flow/runner/enactment/enactment_termination_and_exception_test.exs

@@ -1,5 +1,5 @@
 defmodule ColouredFlow.Runner.Enactment.EnactmentTerminationAndExceptionTest do
-  use ColouredFlow.RepoCase
+  use ColouredFlow.RepoCase, async: true
   use ColouredFlow.RunnerHelpers
 
   import ColouredFlow.MultiSet, only: :sigils

test/coloured_flow/runner/enactment/enactment_test.exs

@@ -1,5 +1,5 @@
 defmodule ColouredFlow.Runner.EnactmentTest do
-  use ColouredFlow.RepoCase
+  use ColouredFlow.RepoCase, async: true
   use ColouredFlow.RunnerHelpers
 
   alias ColouredFlow.Enactment.BindingElement

test/coloured_flow/runner/enactment/integration_tests/constants_test.exs

@@ -1,5 +1,5 @@
 defmodule ColouredFlow.Runner.Enactment.IntegrationTests.ConstantsTest do
-  use ColouredFlow.RepoCase
+  use ColouredFlow.RepoCase, async: true
   use ColouredFlow.RunnerHelpers
 
   alias ColouredFlow.Enactment.BindingElement

test/coloured_flow/runner/enactment/integration_tests/pattern_match_on_complex_tokens_test.exs

@@ -1,5 +1,5 @@
 defmodule ColouredFlow.Runner.Enactment.IntegrationTests.PatternMatchOnComplexTokensTest do
-  use ColouredFlow.RepoCase
+  use ColouredFlow.RepoCase, async: true
   use ColouredFlow.RunnerHelpers
 
   alias ColouredFlow.Enactment.BindingElement

test/coloured_flow/runner/enactment/integration_tests/reuse_workitems_test.exs

@@ -1,5 +1,5 @@
 defmodule ColouredFlow.Runner.Enactment.IntegrationTests.ReuseWorkitemsTest do
-  use ColouredFlow.RepoCase
+  use ColouredFlow.RepoCase, async: true
   use ColouredFlow.RunnerHelpers
 
   alias ColouredFlow.Enactment.BindingElement

test/coloured_flow/runner/enactment/integration_tests/transition_without_input_places_test.exs

@@ -1,5 +1,5 @@
 defmodule ColouredFlow.Runner.Enactment.IntegrationTests.TransitionWithoutInputPlacesTest do
-  use ColouredFlow.RepoCase
+  use ColouredFlow.RepoCase, async: true
   use ColouredFlow.RunnerHelpers
 
   alias ColouredFlow.Enactment.BindingElement

test/coloured_flow/runner/enactment/integration_tests/transition_without_output_places_test.exs

@@ -1,5 +1,5 @@
 defmodule ColouredFlow.Runner.Enactment.IntegrationTests.TransitionWithoutOutputPlacesTest do
-  use ColouredFlow.RepoCase
+  use ColouredFlow.RepoCase, async: true
   use ColouredFlow.RunnerHelpers
 
   alias ColouredFlow.Enactment.BindingElement

test/coloured_flow/runner/enactment/integration_tests/transition_without_token_consumed_test.exs

@@ -1,5 +1,5 @@
 defmodule ColouredFlow.Runner.Enactment.IntegrationTests.TransitionWithoutTokenConsumedTest do
-  use ColouredFlow.RepoCase
+  use ColouredFlow.RepoCase, async: true
   use ColouredFlow.RunnerHelpers
 
   alias ColouredFlow.Enactment.BindingElement

test/coloured_flow/runner/enactment/integration_tests/transition_without_token_produced_test.exs

@@ -1,5 +1,5 @@
 defmodule ColouredFlow.Runner.Enactment.IntegrationTests.TransitionWithoutTokenProducedTest do
-  use ColouredFlow.RepoCase
+  use ColouredFlow.RepoCase, async: true
   use ColouredFlow.RunnerHelpers
 
   alias ColouredFlow.Enactment.BindingElement