feat: make BasicBlock::new publicly accessible

[fuqiuluo]

Description

Makes the BasicBlock::new method publicly accessible by changing its visibility from pub(crate) to pub.

Motivation

Currently, the BasicBlock::new method is only accessible within the crate, which limits external users' ability to create BasicBlock instances directly from LLVMBasicBlockRef. This change allows users to have more direct control over BasicBlock creation when working with LLVM C API interop scenarios.

Changes

• Changed visibility of BasicBlock::new from pub(crate) to pub in src/basic_block.rs

Checklist

• I am basing my changes off master
• I have run cargo clippy and updated portions of code pertaining to my changes
• I will keep my code reasonably up to date via rebasing over merging whenever possible

Notes

This is a non-breaking change that only expands the public API surface. The method signature and behavior remain unchanged - it still safely handles null pointer checks and returns Option<Self>.

[TheDan64]

Thanks!

[TheDan64]

@fuqiuluo please add a doc comment to the method; thanks!

[fuqiuluo]

done! add a doc comment