[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>

cpmfile.json

@@ -301,17 +301,6 @@
         "repo": "eden-emu/tzdb_to_nx",
         "version": "230326"
     },
-    "unordered-dense": {
-        "bundled": true,
-        "find_args": "CONFIG",
-        "hash": "d2106f6640f6bfb81755e4b8bfb64982e46ec4a507cacdb38f940123212ccf35a20b43c70c6f01d7bfb8c246d1a16f7845d8052971949cea9def1475e3fa02c8",
-        "package": "unordered_dense",
-        "patches": [
-            "0001-avoid-memset-when-clearing-an-empty-table.patch"
-        ],
-        "repo": "martinus/unordered_dense",
-        "version": "7b55cab841"
-    },
     "vulkan-headers": {
         "hash": "d2846ea228415772645eea4b52a9efd33e6a563043dd3de059e798be6391a8f0ca089f455ae420ff22574939ed0f48ed7c6ff3d5a9987d5231dbf3b3f89b484b",
         "min_version": "1.4.317",