Remove usingnamespace usage, build script fixups, and support linking memory allocation functions from a shared library

[kcbanner]

Supersedes #5.

As of 0.15.x usingnamespace has been removed: ziglang/zig#20663

Changes:

• Remove usingnamespace usage
• Fixup build script / callconv deprecations
• Use the new @extern field, .is_dll_import, to allow linking the memory allocation functions from a shared library when using the -msvc ABI
• Alignment fixup
• Change appendMeshPrimitive to use unmanaged data structures (managed versions are being deprecated)

[Copilot]

Pull Request Overview

This PR modernizes the zmesh library to be compatible with Zig 0.15.x by removing deprecated usingnamespace declarations and updating various syntax elements. The changes primarily involve moving functionality from the io module to the zcgltf module, updating calling conventions, and modernizing memory allocation patterns.

• Remove usingnamespace usage and reorganize module structure
• Update calling conventions from .C to .c and use new @extern syntax with .is_dll_import
• Modernize data structures to use unmanaged versions and update alignment syntax

Reviewed Changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
src/zcgltf.zig	Moves functions from io.zig and updates calling conventions to .c
src/memory.zig	Updates @extern declarations with new syntax and modernizes alignment handling
src/io.zig	Removes usingnamespace and delegates to zcgltf module
src/Shape.zig	Updates ArrayList usage to use explicit allocator parameter
build.zig.zon	Updates minimum Zig version requirement to 0.15.1
build.zig	Modernizes build script syntax and library creation
README.md	Updates examples to use unmanaged data structures

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