refactor!: improve support for ec2 instance workers

Problem:

The PosixInstanceWorker and WindowsInstanceWorker classes implement a
CMF Worker based on an ec2 host. In both cases they start with an empty
AMI image (AL2023 or Win Server 2022) then set up users, install the
agent, etc. Tests that need to use an AMI that already has users and the
agent installed end up having to hack around a lot of assumptions in
these classes, or reimplement everything for an ec2-based worker from
scratch.

Solution:

Refactor the PosixInstanceWorker and WindowsInstanceWorker to split them
into os-specific base classes that contain all of the generic worker
implementation stuff (starting the worker, getting its id, etc), and a
derived class that implements the user-setup, agent install, and the
like. This makes space for tests that use an AMI with the users & agent
pre-setup to derive from the os-specific base classes to get the generic
ec2-worker test functionality.

BREAKING CHANGE: PosixInstanceWorker has been renamed to
PosixInstanceBuildWorker, and WindowsInstanceWorker has been renamed to
WindowsInstanceBuildWorker.

src/deadline_test_fixtures/__init__.py

@@ -7,8 +7,10 @@
     DeadlineWorkerConfiguration,
     DockerContainerWorker,
     EC2InstanceWorker,
-    WindowsInstanceWorker,
-    PosixInstanceWorker,
+    WindowsInstanceWorkerBase,
+    WindowsInstanceBuildWorker,
+    PosixInstanceWorkerBase,
+    PosixInstanceBuildWorker,
     Job,
     Farm,
     Fleet,
@@ -53,8 +55,10 @@
     "DeadlineWorkerConfiguration",
     "DockerContainerWorker",
     "EC2InstanceWorker",
-    "WindowsInstanceWorker",
-    "PosixInstanceWorker",
+    "WindowsInstanceWorkerBase",
+    "WindowsInstanceBuildWorker",
+    "PosixInstanceWorkerBase",
+    "PosixInstanceBuildWorker",
     "Farm",
     "Fleet",
     "Job",

src/deadline_test_fixtures/deadline/__init__.py

@@ -16,8 +16,10 @@
     DeadlineWorkerConfiguration,
     DockerContainerWorker,
     EC2InstanceWorker,
-    PosixInstanceWorker,
-    WindowsInstanceWorker,
+    PosixInstanceWorkerBase,
+    PosixInstanceBuildWorker,
+    WindowsInstanceWorkerBase,
+    WindowsInstanceBuildWorker,
     PipInstall,
 )
 
@@ -29,8 +31,10 @@
     "DeadlineWorkerConfiguration",
     "DockerContainerWorker",
     "EC2InstanceWorker",
-    "WindowsInstanceWorker",
-    "PosixInstanceWorker",
+    "WindowsInstanceWorkerBase",
+    "WindowsInstanceBuildWorker",
+    "PosixInstanceWorkerBase",
+    "PosixInstanceBuildWorker",
     "Farm",
     "Fleet",
     "Job",