Code cleanup (backport #1217)

[mergify]

🦟 Bug fix

Fixes #

Summary

Various code cleanup and fixes:

• unnecessary copying (e.g. in range-for loop or from iterator)
• code simplification (like std::string().compare("..") vs operator == or do-while loop replaced by range-for)
• fixed CppCheck warning in RenderPassByIndex
• fixed CppCheck warning of hiding: engine local variable vs engine function in the same namespace
• clarified counter type for textures (auto i = 0u will produce unsinged int, but it should be uint64_t) and some other loops
• raii for std::mutex (behaviour should be the same, just safer approach, at least in callbacks)
• define -> constexpr
• GZ_ASSERT to static_assert due to we comparing 2 compile-time constants
• typos

Nothing outstanding or interesting

Checklist

• Signed all commits for DCO
• Added tests
• Updated documentation (as needed)
• Updated migration guide (as needed)
• Consider updating Python bindings (if the library has them)
• codecheck passed (See contributing)
• All tests passed (See test coverage)
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This is an automatic backport of pull request #1217 done by [Mergify](https://mergify.com).