feat(isolation): process isolation for custom nodes via pyisolate

Adds opt-in process isolation for custom nodes using pyisolate's
bwrap sandbox and JSON-RPC bridge. Each isolated node pack runs in
its own child process with zero-copy tensor transfer via shared memory.

Core infrastructure:
- CLI flag --use-process-isolation to enable isolation
- Host/child startup fencing via PYISOLATE_CHILD env var
- Manifest-driven node discovery and extension loading
- JSON-RPC bridge between host and child processes
- Shared memory forensics for leak detection

Proxy layer:
- ModelPatcher, CLIP, VAE, and ModelSampling proxies
- Host service proxies (folder_paths, model_management, progress, etc.)
- Proxy base with automatic method forwarding

Execution integration:
- Extension wrapper with V3 hidden param mapping
- Runtime helpers for isolated node execution
- Host policy for node isolation decisions
- Fenced sampler device handling and model ejection parity

Serializers for cross-process data transfer:
- File3D (GLB), PLY (structured + gaussian), NPZ (streaming frames),
  VIDEO (VideoFromFile + VideoFromComponents) serializers
- data_type flag in SerializerRegistry for type-aware dispatch
- Isolated get_temp_directory() fence

New core save nodes:
- SavePLY and SaveNPZ with comfytype registrations (Ply, Npz)

DynamicVRAM compatibility:
- comfy-aimdo early init gated by isolation fence

Tests:
- Integration and policy tests for isolation lifecycle
- Manifest loader, host policy, proxy, and adapter unit tests

Depends on: pyisolate >= 0.9.2

comfy/k_diffusion/sampling.py

@@ -1,4 +1,5 @@
 import math
+import os
 from functools import partial
 
 from scipy import integrate
@@ -12,8 +13,8 @@ from . import deis
 from . import sa_solver
 import comfy.model_patcher
 import comfy.model_sampling
-
 import comfy.memory_management
+from comfy.cli_args import args
 from comfy.utils import model_trange as trange
 
 def append_zero(x):
@@ -191,6 +192,13 @@ def sample_euler(model, x, sigmas, extra_args=None, callback=None, disable=None,
     """Implements Algorithm 2 (Euler steps) from Karras et al. (2022)."""
     extra_args = {} if extra_args is None else extra_args
     s_in = x.new_ones([x.shape[0]])
+    isolation_active = args.use_process_isolation or os.environ.get("PYISOLATE_CHILD") == "1"
+    if isolation_active:
+        target_device = sigmas.device
+        if x.device != target_device:
+            x = x.to(target_device)
+        s_in = s_in.to(target_device)
+
     for i in trange(len(sigmas) - 1, disable=disable):
         if s_churn > 0:
             gamma = min(s_churn / (len(sigmas) - 1), 2 ** 0.5 - 1) if s_tmin <= sigmas[i] <= s_tmax else 0.