chore: enable pyupgrade fixes (#1806)

# What does this PR do?

The goal of this PR is code base modernization.

Schema reflection code needed a minor adjustment to handle UnionTypes
and collections.abc.AsyncIterator. (Both are preferred for latest Python
releases.)

Note to reviewers: almost all changes here are automatically generated
by pyupgrade. Some additional unused imports were cleaned up. The only
change worth of note can be found under `docs/openapi_generator` and
`llama_stack/strong_typing/schema.py` where reflection code was updated
to deal with "newer" types.

Signed-off-by: Ihar Hrachyshka <ihar.hrachyshka@gmail.com>

llama_stack/models/llama/llama3/model.py

@@ -5,7 +5,6 @@
 # the root directory of this source tree.
 
 import math
-from typing import Optional, Tuple
 
 import fairscale.nn.model_parallel.initialize as fs_init
 import torch
@@ -80,7 +79,7 @@ def apply_rotary_emb(
     xq: torch.Tensor,
     xk: torch.Tensor,
     freqs_cis: torch.Tensor,
-) -> Tuple[torch.Tensor, torch.Tensor]:
+) -> tuple[torch.Tensor, torch.Tensor]:
     xq_ = torch.view_as_complex(xq.float().reshape(*xq.shape[:-1], -1, 2))
     xk_ = torch.view_as_complex(xk.float().reshape(*xk.shape[:-1], -1, 2))
     freqs_cis = reshape_for_broadcast(freqs_cis, xq_)
@@ -162,7 +161,7 @@ class Attention(nn.Module):
         x: torch.Tensor,
         start_pos: int,
         freqs_cis: torch.Tensor,
-        mask: Optional[torch.Tensor],
+        mask: torch.Tensor | None,
     ):
         bsz, seqlen, _ = x.shape
         xq, xk, xv = self.wq(x), self.wk(x), self.wv(x)
@@ -204,7 +203,7 @@ class FeedForward(nn.Module):
         dim: int,
         hidden_dim: int,
         multiple_of: int,
-        ffn_dim_multiplier: Optional[float],
+        ffn_dim_multiplier: float | None,
     ):
         super().__init__()
         hidden_dim = int(2 * hidden_dim / 3)
@@ -243,7 +242,7 @@ class TransformerBlock(nn.Module):
         x: torch.Tensor,
         start_pos: int,
         freqs_cis: torch.Tensor,
-        mask: Optional[torch.Tensor],
+        mask: torch.Tensor | None,
     ):
         h = x + self.attention(self.attention_norm(x), start_pos, freqs_cis, mask)
         out = h + self.feed_forward(self.ffn_norm(h))