style: ruff's own fixes, mechanically applied

`ruff check .` had gone unrun long enough to report 568 errors, which is the
same as having no linter: the next real finding would have been invisible in the
noise. This is the 521 it fixes by itself, in 173 files, and nothing else — the
98 it cannot fix are the next commit.

What actually changed: import sorting (225), imports nobody used (87, none of
them a re-export — no `__init__.py` is touched, which was the one way this could
have broken an import elsewhere), `datetime.timezone.utc` to `datetime.UTC` (69)
and `asyncio.TimeoutError` to `TimeoutError` (18), both plain aliases on the 3.12
this project requires, `Optional[X]` to `X | None` (24), and f-strings with
nothing to interpolate (19).

Checked rather than assumed: every module in the three packages still imports,
and the suite is 2893 passed — the same count, test for test, as the merge
before it.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

1 files changed, 4 insertions, 2 deletions

diff --git a/packages/meshbay-common/src/meshbay_common/keyderive.py b/packages/meshbay-common/src/meshbay_common/keyderive.py
index 497f877..4b90af3 100644
--- a/packages/meshbay-common/src/meshbay_common/keyderive.py
+++ b/packages/meshbay-common/src/meshbay_common/keyderive.py
@@ -24,11 +24,11 @@ See keyderive.js for the browser-side implementation.
 """
 
 import hashlib
+
 from cryptography.hazmat.primitives.asymmetric.ed25519 import Ed25519PrivateKey
 from cryptography.hazmat.primitives.asymmetric.x25519 import X25519PrivateKey
 from cryptography.hazmat.primitives.kdf.argon2 import Argon2id
 
-
 # Argon2id parameters — same as keystore (see crypto.py)
 _ITERATIONS  = 3
 _MEMORY_COST = 65536   # 64 MB — increase to 262144 for production
@@ -85,9 +85,11 @@ def encrypt_keypair_bundle(
     Returns: AES-256-GCM ciphertext (nonce prepended).
     """
     import os
+
+    import msgpack
     from cryptography.hazmat.primitives.ciphers.aead import AESGCM
+
     from meshbay_common.crypto import sk_to_raw
-    import msgpack
 
     # Derive an AES key from the password (different info string from key derivation)
     salt = hashlib.sha256(f"meshbay:bundle:v1:{username}".encode()).digest()