ci: Use codex produced v8 artifacts for release builds (#23934)

Updates our build script to pull down the artifacts like we do in CI for
building v8 into our targets.

This changes the flow so that we now pre-install rusty v8 assets for all
of our release targets from pre-built in workflow.
Secondarily if running it locally we now optionally pull the assets down
on python run assuming the user hasn't set the proper values, it then
provides them.

Sorry for the miss here.

scripts/codex_package/cargo.py

@@ -8,6 +8,7 @@ from pathlib import Path
 from .targets import REPO_ROOT
 from .targets import PackageVariant
 from .targets import TargetSpec
+from .v8 import resolve_codex_v8_cargo_env
 
 
 CODEX_RS_ROOT = REPO_ROOT / "codex-rs"
@@ -60,8 +61,19 @@ def build_source_binaries(
         for binary in binaries:
             cmd.extend(["--bin", binary])
 
+        cargo_env = None
+        if entrypoint_bin is None:
+            codex_v8_env = resolve_codex_v8_cargo_env(spec)
+            if codex_v8_env:
+                cargo_env = {**os.environ, **codex_v8_env}
+
         print("+", " ".join(cmd))
-        subprocess.run(cmd, cwd=CODEX_RS_ROOT, check=True)
+        subprocess.run(
+            cmd,
+            cwd=CODEX_RS_ROOT,
+            check=True,
+            env=cargo_env,
+        )
 
     output_dir = cargo_profile_output_dir(spec, profile)
     outputs = SourceBuildOutputs(