[common] Switch to boost::unordered_flat containers (#4326)

Replaces all instances of ankerl's unordered map/set with boost's
`unordered_flat_*` classes. This uses std::hash since boost::hash is
actually a lot slower.

Also adds an abstraction layer in `Common` so future changes are quicker
and easier.

Other implementation details:
- ankerl provided hash specializations for tuple and pair, so those were
  ported here
- std::erase_if doesn't work on boost, so just used the ADL'd erase_if

This should be about equal or superior performance as unordered_dense for everything except iteration.

Signed-off-by: crueter <crueter@eden-emu.dev>

- [x] I have read and followed the [Contribution Guidelines](https://git.eden-emu.dev/eden-emu/eden/src/branch/master/CONTRIBUTING.md#code-contributions).
- [x] I have read and followed the [AI Policy](https://git.eden-emu.dev/eden-emu/eden/src/branch/master/docs/policies/AI.md)
- [x] I have read and followed the [Coding Guidelines](https://git.eden-emu.dev/eden-emu/eden/src/branch/master/docs/policies/Coding.md) to the best of my ability.

-------------------

Reviewed-on: https://git.eden-emu.dev/eden-emu/eden/pulls/4326
Reviewed-by: Lizzie and Samuel <lizzie@eden-emu.dev>
Reviewed-by: MaranBr <maranbr@eden-emu.dev>

src/common/CMakeLists.txt

@@ -147,7 +147,8 @@ add_library(
     cpu_features.cpp
     cpu_features.h
     httplib.h
-    net/net.h net/net.cpp)
+    net/net.h net/net.cpp
+    container/unordered_map.h container/unordered_set.h)
 
 if(WIN32)
     target_sources(common PRIVATE windows/timer_resolution.cpp
@@ -241,7 +242,7 @@ if (lz4_ADDED)
     target_include_directories(common PRIVATE ${lz4_SOURCE_DIR}/lib)
 endif()
 
-target_link_libraries(common PUBLIC fmt::fmt stb::headers Threads::Threads unordered_dense::unordered_dense)
+target_link_libraries(common PUBLIC fmt::fmt stb::headers Threads::Threads)
 target_link_libraries(common PRIVATE lz4::lz4 zstd::zstd)
 
 # Please refer to src/common/demangle.cpp