implement minor improvements in existing code

[mick-lue]

Going through the code, I encountered a few instances where minor improvements can be made.

tree_container.h

• std::format avoids creating temporary strings that then get concatenated, allowing the compiler to do in-place string construction.

winapi

• we can pass the path object as a const reference to avoid copying it for the (recursive) function call createPath.

ttrampolinepool.cpp

• using try_emplace instead of insert allows creating the pair in-place without instantiating a local object first. It will also instantiate a default BufferList() as before, but I added a comment to make it clear
• using buffers.empty() can be more efficient than comparing to buffers.size() depending on the implementation of size() and makes the code easier to understand
• using !m_ThreadGuards->contains(func) makes the code easier to understand

hookmanager.cpp

• try_emplace allows in-place construction

maptracker.h

• see winapi, same code for createFakePath as createPath
• the explicit call to std::move when returning a local variable prevents the compiler from doing copy elision optimizations here. Without it, the compiler can potentially further optimize the function.

usvfs.cpp

• using constant references to the library strings prevents temporary copies of those strings
• as RedirectionTree::exists accepts a string_view there is no need to transform the iterator string to a c_str.

Tests

All tests still pass and I've had no issues using MO2, starting programs or games through MO2 and playing heavily-modded skyrirm for example.