refactor: Replace unsafe methods with safe methods for certificate handler

[0x676e67]

This pull request includes several changes to improve the handling of certificate compression and update dependencies. The most important changes include updating the boring2 dependency, removing the cert/compression.rs module, and refactoring related code.

Dependency updates:

• Updated boring2 to version 4.15.2 and added the cert-compression feature. Removed boring-sys2 dependency. (Cargo.toml)

Code refactoring:

• Removed the cert/compression.rs module, along with the CertCompressionAlgorithm enum and related functions. (src/tls/cert/compression.rs)
• Refactored imports and usage of CertCompressionAlgorithm in various modules to align with the removal of cert/compression.rs. (src/imp/mod.rs, src/lib.rs, src/tls/ext.rs, src/tls/mod.rs) [1] [2] [3] [4]

Simplification of certificate store handling:

• Replaced direct usage of ffi functions with higher-level methods from the boring2 crate for setting certificate stores. (src/tls/cert/mod.rs) [1] [2]…ndler