feat: add the codec support

[chlins]

This pull request introduces significant changes to the modctl package, focusing on replacing the archiver package with a new codec package for encoding and decoding files. Additionally, it updates the model-spec dependency and refactors various functions to integrate the new codec system.

Dependency updates:

• Updated github.com/CloudNativeAI/model-spec from v0.0.2 to v0.0.3 in go.mod.

Refactoring and integration of codec package:

• Replaced archiver package with codec package in pkg/backend/build/builder.go. The OutputLayer method signature and the BuildLayer function were updated to use the new codec system for encoding files. [1] [2] [3] [4]
• Updated OutputLayer method in pkg/backend/build/local.go to use the new codec system.
• Updated OutputLayer method in pkg/backend/build/remote.go to use the new codec system. [1] [2]
• Replaced archiver package with codec package in pkg/backend/extract.go and refactored the exportModelArtifact function to use the new codec system for extracting layers. [1] [2]
• Replaced archiver package with codec package in pkg/backend/pull.go and updated the pullAndExtractFromRemote function to use the new codec system for extracting layers. [1] [2]

Introduction of codec package:

• Added a new codec package with Codec, RawCodec, and TarCodec implementations for encoding and decoding files. [1] [2] [3]

[gaius-qi]

LGTM