add codec.Codec

[ajiyoshi-vg]

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[Copilot]

PR Overview

This pull request introduces a generic Codec interface along with a JSON codec implementation and corresponding tests. Key changes include:

• Adding the Codec interface in codec/codec.go.
• Implementing the generic JSON codec in codec/json.go.
• Creating tests in codec/json_test.go.
• Refactoring chunkfile.go to use the new codec for storing and restoring data.

Reviewed Changes

File	Description
codec/json_test.go	Adds tests to verify the JSON codec functionality.
codec/json.go	Implements a generic JSON codec with Encode and Decode methods.
codec/codec.go	Introduces the Codec interface definition.
chunkfile.go	Updates data store/restore logic to use the new codec implementation.

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

Comments suppressed due to low confidence (1)

codec/json.go:31

• [nitpick] Using log.Printf for error reporting in the Decode method may obscure decoding issues; consider propagating the error instead to better inform the caller.

log.Printf("decode failed: %v", err)