chore: hoist lazy import struct to module level in tuples.py

The V1 params tuple encode/decode paths had `import struct` inside
function bodies, unlike every other module that imports struct at the
top level. Hoisted to module level for consistency and to avoid the
sys.modules lookup on every V1 call.

Closes #135

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: antoineleclair

src/dqlitewire/tuples.py

@@ -5,6 +5,7 @@
 - Row tuples: column types header, then values
 """
 
+import struct
 from collections.abc import Sequence
 from enum import Enum
 from typing import Any
@@ -57,8 +58,6 @@ def encode_params_tuple(params: Sequence[Any], schema: int = 0, buffer_offset: i
     header = bytearray()
     if schema == 1:
         # V1: uint32 count
-        import struct
-
         header.extend(struct.pack("<I", len(params)))
     else:
         # V0: uint8 count
@@ -120,8 +119,6 @@ def decode_params_tuple(
     count_size: int
     if count is None:
         if schema == 1:
-            import struct
-
             count = struct.unpack("<I", data[:4])[0]
             count_size = 4
         else: