feat:Add AES-GCM encryption and decryption utilities with tests

[betterlmy]

This pull request introduces AES-GCM encryption and decryption utilities to the secutil package, along with comprehensive tests to ensure correct functionality and error handling. The most important changes are grouped below:

AES-GCM Encryption/Decryption Implementation:

• Added the EncryptGCM and DecryptGCM functions to aes_gcm.go for encrypting and decrypting data using AES-GCM, including random nonce generation and key validation.
• Introduced error variables ErrInvalidAESKeySize and ErrInvalidGCMNonceSize for precise error reporting on invalid key and nonce sizes.

Testing and Validation:

• Added aes_gcm_test.go with tests covering valid AES key sizes, empty plaintext handling, and error cases for invalid key and nonce sizes, ensuring robust functionality and edge case coverage.
• Tests verify that decryption fails with incorrect keys or nonce sizes, and that encryption rejects invalid key lengths.

[Copilot]

Pull request overview

This PR adds AES-GCM encryption/decryption helpers to the x/encodes/secutil package, along with unit tests to validate round-trip behavior and key/nonce validation.

Changes:

• Introduced EncryptGCM and DecryptGCM utilities backed by crypto/cipher AES-GCM.
• Added sentinel errors for invalid AES key sizes and invalid GCM nonce sizes.
• Added tests covering valid AES key sizes, empty plaintext, and invalid key/nonce error paths.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
x/encodes/secutil/aes_gcm.go	Adds AES-GCM encrypt/decrypt helpers with key-size validation and nonce generation.
x/encodes/secutil/aes_gcm_test.go	Adds unit tests for round-trip encryption/decryption and error handling.

[betterlmy]

Hi @inhere, please take a look at this PR when you have a moment. Thanks!