update invalid boundary error message

Author: zefir-git

src/Multipart.ts

@@ -65,7 +65,7 @@ export class Multipart implements Part {
     public constructor(public readonly parts: Part[], boundary: Uint8Array | string = crypto.randomUUID(), mediaType: string = "multipart/mixed") {
         this.#boundary = typeof boundary === "string" ? new TextEncoder().encode(boundary) : boundary;
         if (!Multipart.isValidBoundary(this.#boundary))
-            throw new RangeError("Boundary must be 1 to 70 characters long, not end with space, and may only contain: A-Z a-z 0-9 '()+_,-./:=? and space");
+            throw new RangeError("Invalid boundary: must be 1 to 70 characters long, not end with space, and may only contain: A-Z a-z 0-9 '()+_,-./:=? and space");
         this.#mediaType = mediaType;
         this.setHeaders();
     }
@@ -121,7 +121,7 @@ export class Multipart implements Part {
     public set boundary(boundary: Uint8Array | string) {
         this.#boundary = typeof boundary === "string" ? new TextEncoder().encode(boundary) : boundary;
         if (!Multipart.isValidBoundary(this.#boundary))
-            throw new RangeError("Boundary must be 1 to 70 characters long, not end with space, and may only contain: A-Z a-z 0-9 '()+_,-./:=? and space");
+            throw new RangeError("Invalid boundary: must be 1 to 70 characters long, not end with space, and may only contain: A-Z a-z 0-9 '()+_,-./:=? and space");
         this.setHeaders();
     }