fix(escrow-native): prevent rent refund redirection

[yukikm]

Fixes two issues in tokens/escrow/native:

1. Security: prevent taker from redirecting the offer account rent refund to an attacker-controlled payer account. The rent is now refunded to the maker (offer initializer).
2. Correctness: fix post-transfer balance assertion (was using the wrong pre-transfer variable).

Adds a regression test proving the rent refund cannot be redirected.

[Copilot]

Pull request overview

This PR addresses critical security vulnerabilities related to lamport manipulation in Solana programs. The primary focus is on the escrow native program, with additional security hardening in the transfer-sol anchor example.

Changes:

• Fixed rent refund redirection vulnerability in escrow: rent from closed offer accounts now goes to the maker (initializer) instead of an arbitrary payer
• Corrected post-transfer balance assertion bug in escrow that was checking the wrong variable
• Enhanced transfer-sol/anchor with signer validation and overflow protection for direct lamport transfers

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
tokens/escrow/native/program/src/instructions/take_offer.rs	Refunds offer rent to maker instead of payer; fixes balance assertion to use correct pre-transfer variable
tokens/escrow/native/tests/instruction.ts	Makes maker account writable to receive rent refund
tokens/escrow/native/tests/test.ts	Adds comprehensive regression test proving rent cannot be redirected to attacker-controlled payer
basics/transfer-sol/anchor/programs/transfer-sol/src/lib.rs	Adds Signer constraint, checked arithmetic for overflow protection, and explicit balance validation
basics/transfer-sol/anchor/tests/test.ts	Adds required signer to match updated program constraints

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[yukikm]

Note: GitHub Copilot “Pull request overview” currently mentions changes under basics/transfer-sol/..., but the current PR head only touches escrow-native (3 files).

Source of truth patch (shows the actual diff):
https://github.com/solana-developers/program-examples/pull/533.patch