[BUG] Check env in benchmarking script (#3297)

Using `ctx.get_or_create_runner` in benchmarking warmup code / metrics
builder causes subsequent `ray.inits` to crash. Just check the
`DAFT_RUNNER` environment var instead, which should be set.

Tested:
- local ->
https://github.com/Eventual-Inc/daft-benchmarking/actions/runs/11838323155
- remote ->
https://github.com/Eventual-Inc/daft-benchmarking/actions/runs/11838783067

---------

Co-authored-by: Colin Ho <[email protected]>

benchmarking/tpch/__main__.py

@@ -12,14 +12,13 @@
 import subprocess
 import warnings
 from datetime import datetime, timezone
-from typing import Any, Callable
+from typing import Any, Callable, Literal
 
 import ray
 
 import daft
 from benchmarking.tpch import answers, data_generation
 from daft import DataFrame
-from daft.context import get_context
 from daft.runners.profiler import profiler
 
 logger = logging.getLogger(__name__)
@@ -130,8 +129,7 @@ def run_all_benchmarks(
 ):
     get_df = get_df_with_parquet_folder(parquet_folder)
 
-    daft_context = get_context()
-    metrics_builder = MetricsBuilder(daft_context.get_or_create_runner().name)
+    metrics_builder = MetricsBuilder(get_daft_benchmark_runner_name())
 
     for i in questions:
         # Run as a Ray Job if dashboard URL is provided
@@ -194,6 +192,16 @@ def get_daft_version() -> str:
     return daft.get_version()
 
 
+def get_daft_benchmark_runner_name() -> Literal["ray"] | Literal["py"] | Literal["native"]:
+    """Test utility that checks the environment variable for the runner that is being used for the benchmarking"""
+    name = os.getenv("DAFT_RUNNER")
+    assert name is not None, "Tests must be run with $DAFT_RUNNER env var"
+    name = name.lower()
+
+    assert name in {"ray", "py", "native"}, f"Runner name not recognized: {name}"
+    return name
+
+
 def get_ray_runtime_env(requirements: str | None) -> dict:
     runtime_env = {
         "py_modules": [daft],
@@ -210,13 +218,10 @@ def get_ray_runtime_env(requirements: str | None) -> dict:
 
 def warmup_environment(requirements: str | None, parquet_folder: str):
     """Performs necessary setup of Daft on the current benchmarking environment"""
-    ctx = daft.context.get_context()
-
-    if ctx.get_or_create_runner().name == "ray":
+    if get_daft_benchmark_runner_name() == "ray":
         runtime_env = get_ray_runtime_env(requirements)
 
         ray.init(
-            address=ctx._runner.ray_address,
             runtime_env=runtime_env,
         )