fix(builtin): uint16 aligned fastpath returns UInt, not UInt16 (#3468)

* fix(builtin): uint16 fastpath returns UInt, not UInt16

The uint16 aligned fastpaths now return UInt (matching the wider
unsafe_extract_uint_le/be convention), so callers don't have to widen.
Drops the .to_uint() step from the int16 variants and the test
cross-checks.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

* test(builtin): swap deprecated UInt::to_int for reinterpret_as_int

Four inspect lines still called the deprecated UInt.to_int() on the
uint16 fastpath results after they started returning UInt.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

* style: moon fmt

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: Yu-zh

builtin/bitstring.mbt

@@ -1077,11 +1077,11 @@ pub fn ArrayView::unsafe_extract_byte_signed_aligned(
 pub fn ArrayView::unsafe_extract_uint16_le_aligned(
   bs : ArrayView[Byte],
   byte_offset : Int,
-) -> UInt16 {
+) -> UInt {
   fixedarray_read_uint16_le(
     buffer_to_fixedarray(bs.buf()),
     bs.start() + byte_offset,
-  )
+  ).to_uint()
 }
 
 ///|
@@ -1090,11 +1090,11 @@ pub fn ArrayView::unsafe_extract_uint16_le_aligned(
 pub fn ArrayView::unsafe_extract_uint16_be_aligned(
   bs : ArrayView[Byte],
   byte_offset : Int,
-) -> UInt16 {
+) -> UInt {
   fixedarray_read_uint16_be(
     buffer_to_fixedarray(bs.buf()),
     bs.start() + byte_offset,
-  )
+  ).to_uint()
 }
 
 ///|
@@ -1104,7 +1104,7 @@ pub fn ArrayView::unsafe_extract_int16_le_aligned(
   bs : ArrayView[Byte],
   byte_offset : Int,
 ) -> Int {
-  bs.unsafe_extract_uint16_le_aligned(byte_offset).to_uint().extend_sign(16)
+  bs.unsafe_extract_uint16_le_aligned(byte_offset).extend_sign(16)
 }
 
 ///|
@@ -1114,7 +1114,7 @@ pub fn ArrayView::unsafe_extract_int16_be_aligned(
   bs : ArrayView[Byte],
   byte_offset : Int,
 ) -> Int {
-  bs.unsafe_extract_uint16_be_aligned(byte_offset).to_uint().extend_sign(16)
+  bs.unsafe_extract_uint16_be_aligned(byte_offset).extend_sign(16)
 }
 
 ///|
@@ -1239,8 +1239,8 @@ pub fn BytesView::unsafe_extract_byte_signed_aligned(
 pub fn BytesView::unsafe_extract_uint16_le_aligned(
   bs : BytesView,
   byte_offset : Int,
-) -> UInt16 {
-  bs.unsafe_read_uint16_le(byte_offset)
+) -> UInt {
+  bs.unsafe_read_uint16_le(byte_offset).to_uint()
 }
 
 ///|
@@ -1249,8 +1249,8 @@ pub fn BytesView::unsafe_extract_uint16_le_aligned(
 pub fn BytesView::unsafe_extract_uint16_be_aligned(
   bs : BytesView,
   byte_offset : Int,
-) -> UInt16 {
-  bs.unsafe_read_uint16_be(byte_offset)
+) -> UInt {
+  bs.unsafe_read_uint16_be(byte_offset).to_uint()
 }
 
 ///|
@@ -1260,7 +1260,7 @@ pub fn BytesView::unsafe_extract_int16_le_aligned(
   bs : BytesView,
   byte_offset : Int,
 ) -> Int {
-  bs.unsafe_read_uint16_le(byte_offset).to_uint().extend_sign(16)
+  bs.unsafe_extract_uint16_le_aligned(byte_offset).extend_sign(16)
 }
 
 ///|
@@ -1270,7 +1270,7 @@ pub fn BytesView::unsafe_extract_int16_be_aligned(
   bs : BytesView,
   byte_offset : Int,
 ) -> Int {
-  bs.unsafe_read_uint16_be(byte_offset).to_uint().extend_sign(16)
+  bs.unsafe_extract_uint16_be_aligned(byte_offset).extend_sign(16)
 }
 
 ///|

builtin/bitstring_test.mbt

@@ -704,19 +704,19 @@ test "aligned fastpath cross-check" {
   // uint16 (2 bytes)
   for b in 0..<=(bytes.length() - 2) {
     assert_eq(
-      aview.unsafe_extract_uint16_le_aligned(b).to_uint(),
+      aview.unsafe_extract_uint16_le_aligned(b),
       aview.unsafe_extract_uint_le(b * 8, 16),
     )
     assert_eq(
-      aview.unsafe_extract_uint16_be_aligned(b).to_uint(),
+      aview.unsafe_extract_uint16_be_aligned(b),
       aview.unsafe_extract_uint_be(b * 8, 16),
     )
     assert_eq(
-      bview.unsafe_extract_uint16_le_aligned(b).to_uint(),
+      bview.unsafe_extract_uint16_le_aligned(b),
       bview.unsafe_extract_uint_le(b * 8, 16),
     )
     assert_eq(
-      bview.unsafe_extract_uint16_be_aligned(b).to_uint(),
+      bview.unsafe_extract_uint16_be_aligned(b),
       bview.unsafe_extract_uint_be(b * 8, 16),
     )
     assert_eq(
@@ -819,10 +819,22 @@ test "aligned fastpath known values" {
   inspect(bview.unsafe_extract_uint_be_aligned(0), content="16909060") // 0x01020304
   inspect(aview.unsafe_extract_uint_le_aligned(0), content="67305985")
   inspect(aview.unsafe_extract_uint_be_aligned(0), content="16909060")
-  inspect(bview.unsafe_extract_uint16_le_aligned(0).to_int(), content="513") // 0x0201
-  inspect(bview.unsafe_extract_uint16_be_aligned(0).to_int(), content="258") // 0x0102
-  inspect(aview.unsafe_extract_uint16_le_aligned(0).to_int(), content="513")
-  inspect(aview.unsafe_extract_uint16_be_aligned(0).to_int(), content="258")
+  inspect(
+    bview.unsafe_extract_uint16_le_aligned(0).reinterpret_as_int(),
+    content="513",
+  ) // 0x0201
+  inspect(
+    bview.unsafe_extract_uint16_be_aligned(0).reinterpret_as_int(),
+    content="258",
+  ) // 0x0102
+  inspect(
+    aview.unsafe_extract_uint16_le_aligned(0).reinterpret_as_int(),
+    content="513",
+  )
+  inspect(
+    aview.unsafe_extract_uint16_be_aligned(0).reinterpret_as_int(),
+    content="258",
+  )
   inspect(
     bview.unsafe_extract_uint64_le_aligned(0) == 0x0807060504030201UL,
     content="true",