More cache improvements (#1015)

* fix rotating kv cache for chat use case

* reorg + fixes to caching, unify prompt caching across types and use cases for e.g. caching during a chat

* nit in chat

* fix tests

* fix tests

* fix tests

* docs

* chat command

* comments + docs

* Define meta_state on all Cache implementations

* fixes + trim_prompt_cache api

* fix default model

---------

Co-authored-by: Angelos Katharopoulos <a_katharopoulos@apple.com>

llms/mlx_lm/models/olmo.py

@@ -1,8 +1,8 @@
 # Copyright © 2023-2024 Apple Inc.
 
+import sys
 from dataclasses import dataclass
-from sys import exit
-from typing import Optional, Tuple
+from typing import Any, Optional, Tuple
 
 import mlx.core as mx
 import mlx.nn as nn
@@ -13,7 +13,7 @@ try:
     import hf_olmo
 except ImportError:
     print("To run olmo install ai2-olmo: pip install ai2-olmo")
-    exit(1)
+    sys.exit(1)
 
 
 @dataclass
@@ -68,7 +68,7 @@ class TransformerBlock(nn.Module):
         self,
         x: mx.array,
         mask: Optional[mx.array] = None,
-        cache: Optional[Tuple[mx.array, mx.array]] = None,
+        cache: Optional[Any] = None,
     ) -> mx.array:
         B, L, D = x.shape
 
@@ -98,7 +98,7 @@ class TransformerBlock(nn.Module):
         self,
         x: mx.array,
         mask: Optional[mx.array] = None,
-        cache: Optional[Tuple[mx.array, mx.array]] = None,
+        cache: Optional[Any] = None,
     ) -> mx.array:
         r = self.attend(self.att_norm(x), mask, cache)
         h = x + r
@@ -174,11 +174,3 @@ class Model(nn.Module):
     @property
     def layers(self):
         return self.model.transformer.blocks
-
-    @property
-    def head_dim(self):
-        return self.args.d_model // self.args.n_heads
-
-    @property
-    def n_kv_heads(self):
-        return self.args.n_heads