feat: support concurrent for build operation(5 concurrency by default)

[chlins]

This pull request introduces several changes to the build process, including the addition of concurrency support and various improvements to the backend processing. The most important changes include adding concurrency options to the build command, updating the backend interface and implementation to support these options, and introducing new processor options.

Build Command Enhancements:

• Added a new flag to specify the number of concurrent build operations (cmd/build.go).
• Updated the runBuild function to pass concurrency options to the backend (cmd/build.go).

Backend Interface and Implementation:

• Modified the Build method in the Backend interface to accept additional options (pkg/backend/backend.go).
• Updated the Build method implementation to apply concurrency options (pkg/backend/build.go). [1] [2] [3]
• Enhanced the process method to support concurrent processing with spinner feedback (pkg/backend/build.go).

Processor Options:

• Introduced a new options struct and associated functions to handle concurrency settings (pkg/backend/processor/options.go).
• Updated various processor implementations to utilize the new concurrency options (pkg/backend/processor/base.go, pkg/backend/processor/code.go, pkg/backend/processor/doc.go, pkg/backend/processor/model.go, pkg/backend/processor/model_config.go). [1] [2] [3] [4] [5] [6] [7] [8] [9] [10]

Dependency Updates:

• Added new dependencies for concurrency and spinner management (go.mod). [1] [2] [3]

Configuration Improvements:

• Added default concurrency settings and validation to the build configuration (pkg/config/build.go).

[gaius-qi]

LGTM