Scope facilitator memo to V2 in 2.0.2

[tony1908]

Summary

• restore legacy V1 memo behavior while keeping the compact facilitator memo convention scoped to the default V2 signing path
• add facilitator memo helpers plus Jest regression coverage for V2 signing and helper parsing behavior
• bump the package to 2.0.2 and document the memo convention as V2-only

Test Plan

• npm test
• npm run build

[gemini-code-assist]

Code Review

This pull request introduces a new Facilitator Memo Convention (V2) for transaction attribution in the x402-stacks SDK. Key changes include the addition of utility functions for creating, normalizing, and parsing facilitator memos, as well as updating the V2 interceptor to adopt this new format. The PR also includes a version bump to 2.0.2, new Jest configuration, and comprehensive test suites for the memo logic. One performance improvement was suggested regarding the implementation of the memo validation utility.

[gemini-code-assist]

The isFacilitatorMemo function creates a new RegExp object on every invocation. Since the prefix is a constant and the nonce pattern is already defined as a constant (FACILITATOR_NONCE_PATTERN), it is more efficient to reuse the existing pattern or perform a string prefix check followed by the nonce validation. This avoids unnecessary object allocation and compilation overhead, which is beneficial if this utility is used in performance-sensitive areas like transaction scanning.

Suggested change

	export function isFacilitatorMemo(memo: string): boolean {
	return new RegExp(`^${FACILITATOR_MEMO_PREFIX}[A-Za-z0-9_-]{24}$`).test(memo);
	}
	export function isFacilitatorMemo(memo: string): boolean {
	return memo.startsWith(FACILITATOR_MEMO_PREFIX) && FACILITATOR_NONCE_PATTERN.test(memo.substring(FACILITATOR_MEMO_PREFIX.length));
	}