memoize inputs and outputs in op/graph snapshots (dagster-io#26482)

Summary:
Iterating through big lists is slow, indexing into a mapping is fast.

Test Plan: BK, speedscope on large multi-asset with many outputs

## Summary & Motivation

## How I Tested These Changes

## Changelog

> Insert changelog entry or delete this section.

python_modules/dagster/dagster/_core/snap/node.py

@@ -1,3 +1,4 @@
+from functools import cached_property
 from typing import Mapping, NamedTuple, Optional, Sequence, Union
 
 import dagster._check as check
@@ -233,6 +234,14 @@ def __new__(
             ),
         )
 
+    @cached_property
+    def input_def_map(self) -> Mapping[str, InputDefSnap]:
+        return {input_def.name: input_def for input_def in self.input_def_snaps}
+
+    @cached_property
+    def output_def_map(self) -> Mapping[str, OutputDefSnap]:
+        return {output_def.name: output_def for output_def in self.output_def_snaps}
+
     def get_input_snap(self, name: str) -> InputDefSnap:
         return _get_input_snap(self, name)
 
@@ -282,6 +291,14 @@ def __new__(
             ),
         )
 
+    @cached_property
+    def input_def_map(self) -> Mapping[str, InputDefSnap]:
+        return {input_def.name: input_def for input_def in self.input_def_snaps}
+
+    @cached_property
+    def output_def_map(self) -> Mapping[str, OutputDefSnap]:
+        return {output_def.name: output_def for output_def in self.output_def_snaps}
+
     def get_input_snap(self, name: str) -> InputDefSnap:
         return _get_input_snap(self, name)
 
@@ -387,18 +404,18 @@ def build_op_def_snap(op_def: OpDefinition) -> OpDefSnap:
 # shared impl for GraphDefSnap and OpDefSnap
 def _get_input_snap(node_def: Union[GraphDefSnap, OpDefSnap], name: str) -> InputDefSnap:
     check.str_param(name, "name")
-    for inp in node_def.input_def_snaps:
-        if inp.name == name:
-            return inp
+    inp = node_def.input_def_map.get(name)
+    if inp:
+        return inp
 
     check.failed(f"Could not find input {name} in op def {node_def.name}")
 
 
 # shared impl for GraphDefSnap and OpDefSnap
 def _get_output_snap(node_def: Union[GraphDefSnap, OpDefSnap], name: str) -> OutputDefSnap:
     check.str_param(name, "name")
-    for out in node_def.output_def_snaps:
-        if out.name == name:
-            return out
+    inp = node_def.output_def_map.get(name)
+    if inp:
+        return inp
 
     check.failed(f"Could not find output {name} in node def {node_def.name}")