SMLib: the prebuilt with eased setbacks

Pins tangency-labs/smlib 56f6e81 (release prebuilt-56f6e811bc84…): smlib_blend_setback_eased
and smlib_blend_setback_open_eased, an ease length before each set-back corner over which a
round's section blends from its circle to the curvature-continuous section (solidcore#1376).
New calls only; existing ones are unchanged (ease 0 is today's body).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

crates/smlib/SMLIB_PREBUILT

@@ -1,10 +1,10 @@
 # Rust target, SHA-256 of smlib-<target>.tar.gz in the release prebuilt-<SMLIB_REV> of
 # tangency-labs/smlib. Written by scripts/fetch-smlib.sh --pin; never edited by hand.
-aarch64-apple-darwin 1831f4bf25b787a5a37bab95cb48836c73886312e87f0b1a4a29bab013e30433
-aarch64-pc-windows-msvc fd8c3826a0b0f84dd6bef4d66b87280026de11ea1cd16e8d90e688f9b7bc11a3
-aarch64-unknown-linux-gnu ce1a857ea1ab4d27ea9577bf70bd0bf18be6416bb7b1d94107e6d92b9558ca83
-i686-pc-windows-msvc 944dab108f28dadb68ade79389cdb2a5fc9e12d1b0331e8b8692a3180c918efc
-wasm32-unknown-unknown 73d69573edb69de53e873d48587905fad6cc4250e5662be3b404c003401f3327
-x86_64-apple-darwin e819a1fb2d069e59d5ac07995af11952ec0c7ef22642f8e714a5e0e0459d21df
-x86_64-pc-windows-msvc 64cb340c1da2cafda86e42556b1dbec9a93fe28908bf3d2b1ec6cd08e15c658e
-x86_64-unknown-linux-gnu b7a2c3f170116e4ab402bb65c8d4851b9a1967617a5049826d578c4c397a2514
+aarch64-apple-darwin e7abaad8909623caee1728cbfbfedbc3d3f1c858e5baa8caef1470809353c5ac
+aarch64-pc-windows-msvc e12cec4931f076bbcc27cc8a892f6c98660440db459e87888f1145bbd8cba1fa
+aarch64-unknown-linux-gnu 816a5a647ba7e06106f6c023a5eaba161b1be47b538575cabb4f0ee16cac1ad0
+i686-pc-windows-msvc a5e7fe9c6ca15475291080eb385a3f7d8ab1a8018523c99b3ab2d26ca58f85db
+wasm32-unknown-unknown ffa2124ae79ac93fc69728ac58b9ee3383ba39779a9cb94be8523f652782700d
+x86_64-apple-darwin 868df2b3f0d1fcf25156998d83a5a47608f14da7461134dc5f96eaa0cd3e7926
+x86_64-pc-windows-msvc fdc3e09310ca87a48ce0ceaca5091d7c11ce55beb9683a2ff350c986c98f3669
+x86_64-unknown-linux-gnu 5179265ede89a2677fe9cd5fb4e92345f7c584432b48c98a03244a6cf5038fb2

crates/smlib/SMLIB_REV

@@ -1 +1 @@
-1072d1b857de2b8d012f09565ad54b2432ff4ddc
+56f6e811bc8491265c75f8e7707c582513ffc738