Reset whole render context in `reset`

sparse_strips/vello_cpu/src/render.rs

diff --git a/sparse_strips/vello_cpu/src/render.rs b/sparse_strips/vello_cpu/src/render.rs
index 7f59892..b291c3e 100644
--- a/sparse_strips/vello_cpu/src/render.rs
+++ b/sparse_strips/vello_cpu/src/render.rs
@@ -151,6 +151,10 @@
 
     /// Reset the render context.
     pub fn reset(&mut self) {
+        self.line_buf.clear();
+        self.tiles.reset();
+        self.alphas.clear();
+        self.strip_buf.clear();
         self.wide.reset();
     }