Switch from borsh to @zorsh/zorsh

Replace the borsh library with @zorsh/zorsh throughout the codebase:

- Update package.json to use @zorsh/zorsh ^0.4.0 instead of borsh 1.0.0
- Convert all schema definitions in src/transactions/schema.ts to use
  zorsh's builder API (b.struct, b.enum, b.bytes, etc.)
- Update serialize/deserialize calls to use schema methods instead of
  standalone functions
- Fix type compatibility issues with type assertions at serialization
  boundaries where needed
- Update test files to use zorsh API

The binary serialization format remains identical as both libraries
implement the Borsh specification.

Author: claude

.changeset/switch-borsh-to-zorsh.md

@@ -0,0 +1,5 @@
+---
+"near-api-js": patch
+---
+
+Replace borsh with @zorsh/zorsh for Borsh serialization (maintains identical binary format)

package.json

@@ -22,7 +22,7 @@
     "dependencies": {
         "depd": "2.0.0",
         "@scure/base": "1.2.4",
-        "borsh": "1.0.0",
+        "@zorsh/zorsh": "^0.4.0",
         "@noble/hashes": "1.7.1",
         "@noble/curves": "1.8.1",
         "secp256k1": "5.0.1",

pnpm-lock.yaml

@@ -8,7 +8,7 @@ import {
     encodeTransaction,
     encodeDelegateAction,
 } from '../transactions/index.js';
-import { Schema, serialize } from 'borsh';
+import { b } from '@zorsh/zorsh';
 import { sha256 } from '@noble/hashes/sha256';
 
 export interface SignMessageParams {
@@ -25,14 +25,12 @@ export interface SignedMessage {
     state?: string; // Optional, applicable to browser wallets (e.g. MyNearWallet). The same state passed in SignMessageParams.
 }
 
-export const Nep413MessageSchema: Schema = {
-    struct: {
-        message: 'string',
-        nonce: { array: { type: 'u8', len: 32 } },
-        recipient: 'string',
-        callbackUrl: { option: 'string' },
-    },
-};
+export const Nep413MessageSchema = b.struct({
+    message: b.string(),
+    nonce: b.bytes(32),
+    recipient: b.string(),
+    callbackUrl: b.option(b.string()),
+});
 
 /**
  * General signing interface, can be used for in memory signing, RPC singing, external wallet, HSM, etc.
@@ -70,8 +68,11 @@ export abstract class Signer {
 
         // 2**31 + 413 == 2147484061
         const PREFIX = 2147484061;
-        const serializedPrefix = serialize('u32', PREFIX);
-        const serializedParams = serialize(Nep413MessageSchema, params);
+        const serializedPrefix = b.u32().serialize(PREFIX);
+        const serializedParams = Nep413MessageSchema.serialize({
+            ...params,
+            callbackUrl: params.callbackUrl ?? null,
+        });
 
         const serializedPayload = new Uint8Array(
             serializedPrefix.length + serializedParams.length