feat: Add .merge() higher-order method (#57)

Author: giraugh

.changeset/easy-rice-create.md

@@ -0,0 +1,5 @@
+---
+"windpipe": minor
+---
+
+Implement Stream.merge()

package.json

@@ -74,5 +74,6 @@
     "dts": {
       "footer": "export = Stream"
     }
-  }
+  },
+  "packageManager": "pnpm@8.14.0+sha1.bb42032ff80dba5f9245bc1b03470d2fa0b7fb2f"
 }