Mark all string parameters as comptime where the C API is expecting string literals.

[jhark]

Pros:

• Prevents mistaken usage of dynamically allocated strings.
• Lets us use static constant memory for the source location data.
• Avoids generating unnecessary writes to source location data whenever starting a zone.
• Matches other Zig Tracy bindings such as the one inside the Zig compiler.

Cons:

• Breaking API change.
• Technically you are allowed to pass non-string literals to these functions, and you might want to if you are dynamically loading code/data containing your strings, or promise to keep your strings allocated until program exit. We could export the raw C API to cover more niche use-cases such as these though.