C++: types.inl make functions inline

[filippobrizzi]

Changelog

Make functions defined in types.inl inline.

Description

This is needed to avoid linker multiple definition errors.

How to reproduce:

• Create a library with two .cpp files
• One file includes reader.hpp and one writer.hpp and both need to define MCAP_IMPLEMENTATION
• File types.inl is included by both compilation units and when linker creates the libraries, the functions from types.inl are defined twice.