chore: update readme and remove dep once_cell

[jmjoy]

This pull request includes several changes across multiple files to improve the codebase and update documentation. The most important changes include the replacement of once_cell with OnceLock, updates to the README.md file, and the removal of once_cell from Cargo.toml dependencies.

Codebase simplification:

• Replaced once_cell::sync::OnceCell with std::sync::OnceLock in phper-test/src/context.rs and phper-test/src/fpm.rs. [1] [2] [3]

Documentation updates:

• Consolidated PHP version support ranges in the README.md file.
• Added a new example link to phper-framework/jieba-php in the README.md file.

Dependency management:

• Removed once_cell from phper/Cargo.toml and phper-test/Cargo.toml dependencies. [1] [2]