Add std feature gate and no_std clip

[solus161]

Description

What's new:

• tokio-related features are now optional;
• Update lib.rs to gate std at module level for consumer.rs, handle.rs, and producer.rs as most units are depend on std dependencies at the moment. Will gate at finer level in the futures;
• Use alloc version of Arc, core version of Debug, Duration;
• Add build with no default feature in Makefile;

Related Issue

• Closes aimdb-sync: std feature gate + no_std flip + CI lane #199

Checklist

• I have read the CONTRIBUTING.md document.
• My code follows the project's coding standards.
• I have added tests to cover my changes.
• All new and existing tests passed (make check).
• I have updated the documentation accordingly.