Simplify build system integration

[MasonRemaley]

Right now, we jump through some hoops to make sure Tracy can be configured globally. Even so, users need to coordinate optimize/target flags and versions of the library.

Once Zig's build system allows overriding build options for packages from the root, none of this will be necessary. We'll be able to merge it all into a single library and make it fully configurable via build options, there won't be any more constants exposed from root, etc.

This will also make it possible to support features like TRACY_NO_EXIT more easily (they need to be set while building, right now our options aren't available until after tracy is built. Zex would benefit from being able to enable this by default.)