refactor: move act under internal

The runner is an application, not a library. `act/model` and
`act/exprparser` were the last packages anything outside this repository
consumed and they now live in actionslib, so nothing needs the rest of
`act` to be importable, and keeping it importable invites the coupling
that was just removed.

Import paths only, the files are unchanged.

Assisted-by: Codet:GPT-5.1-Codex

internal/act/runner/testdata/actions/docker-local/Dockerfile

@@ -0,0 +1,8 @@
+# Container image that runs your code
+FROM node:24-bookworm-slim
+
+# Copies your code file from your action repository to the filesystem path `/` of the container
+COPY entrypoint.sh /entrypoint.sh
+
+# Code file to execute when the docker container starts up (`entrypoint.sh`)
+ENTRYPOINT ["/entrypoint.sh"]

internal/act/runner/testdata/actions/docker-local/action.yml

@@ -0,0 +1,17 @@
+name: 'Hello World'
+description: 'Greet someone and record the time'
+inputs:
+  who-to-greet:  # id of input
+    description: 'Who to greet'
+    required: true
+    default: 'World'
+outputs:
+  time: # id of output
+    description: 'The time we greeted you'
+runs:
+  using: 'docker'
+  image: 'Dockerfile'
+  env:
+    WHOAMI: ${{ inputs.who-to-greet }}
+  args:
+    - ${{ inputs.who-to-greet }}

internal/act/runner/testdata/actions/docker-local/entrypoint.sh

@@ -0,0 +1,8 @@
+#!/bin/sh -l
+
+echo "Hello $1"
+time=$(date)
+echo ::set-output name=time::$time
+echo ::set-output name=whoami::$WHOAMI
+
+echo "SOMEVAR=$1" >>$GITHUB_ENV