Remove NeonEnvBuilder.start() function

It feels wrong to me to start() from the builder object. Surely the
thing you start is the environment itself, not its configuration.

test_runner/fixtures/neon_fixtures.py

@@ -553,10 +553,6 @@ class NeonEnvBuilder:
         self.env = NeonEnv(self)
         return self.env
 
-    def start(self):
-        assert self.env is not None, "environment is not already initialized, call init() first"
-        self.env.start()
-
     def init_start(
         self,
         initial_tenant_conf: Optional[Dict[str, Any]] = None,
@@ -572,7 +568,7 @@ class NeonEnvBuilder:
         Configuring pageserver with remote storage is now the default. There will be a warning if pageserver is created without one.
         """
         env = self.init_configs(default_remote_storage_if_missing=default_remote_storage_if_missing)
-        self.start()
+        env.start()
 
         # Prepare the default branch to start the postgres on later.
         # Pageserver itself does not create tenants and timelines, until started first and asked via HTTP API.

test_runner/performance/test_storage_controller_scale.py

@@ -84,7 +84,7 @@ def test_storage_controller_many_tenants(
     compute_reconfigure_listener.register_on_notify(lambda body: time.sleep(0.01))
 
     env = neon_env_builder.init_configs()
-    neon_env_builder.start()
+    env.start()
 
     # We will intentionally stress reconciler concurrrency, which triggers a warning when lots
     # of shards are hitting the delayed path.

test_runner/regress/test_compatibility.py

@@ -178,7 +178,7 @@ def test_backward_compatibility(
         neon_env_builder.num_safekeepers = 3
         env = neon_env_builder.from_repo_dir(compatibility_snapshot_dir / "repo")
         env.pageserver.allowed_errors.append(ingest_lag_log_line)
-        neon_env_builder.start()
+        env.start()
 
         check_neon_works(
             env,
@@ -265,7 +265,7 @@ def test_forward_compatibility(
         # does not include logs from previous runs
         assert not env.pageserver.log_contains("git-env:" + prev_pageserver_version)
 
-        neon_env_builder.start()
+        env.start()
 
         # ensure the specified pageserver is running
         assert env.pageserver.log_contains("git-env:" + prev_pageserver_version)

test_runner/regress/test_sharding.py

@@ -374,7 +374,7 @@ def test_sharding_split_smoke(
     non_default_tenant_config = {"gc_horizon": 77 * 1024 * 1024}
 
     env = neon_env_builder.init_configs(True)
-    neon_env_builder.start()
+    env.start()
     tenant_id = TenantId.generate()
     timeline_id = TimelineId.generate()
     env.neon_cli.create_tenant(
@@ -1436,7 +1436,7 @@ def test_sharding_unlogged_relation(neon_env_builder: NeonEnvBuilder):
 
     neon_env_builder.num_pageservers = 2
     env = neon_env_builder.init_configs()
-    neon_env_builder.start()
+    env.start()
 
     tenant_id = TenantId.generate()
     timeline_id = TimelineId.generate()
@@ -1475,7 +1475,7 @@ def test_top_tenants(neon_env_builder: NeonEnvBuilder):
     """
 
     env = neon_env_builder.init_configs()
-    neon_env_builder.start()
+    env.start()
 
     tenants = []
     n_tenants = 8