Replace boost and fmt functionality with C++20 features and update CEF

[JonasGilg]

This PR replaces:

• boost::posix_time with std::chrono
• boost::filesystem with std::filesystem
• fmt with std::format

This PR also updates CEF to version 135, to fix some C++ deprecation issues.

This reduces our dependencies and makes the setup of CosmoScout VR easier.

This change requires gcc-13 or Visual Studio 2019. gcc-13 is the default compiler on Ubuntu 24.04. There are some more possible improvements in date time parsing that would require gcc-14, but since this is not the default compiler on any LTS version of Ubuntu I skipped these improvements.

[github-actions]

Pull Request Test Coverage Report for Build 14450067916

Details

• 11 of 206 (5.34%) changed or added relevant lines in 36 files are covered.
• 192 unchanged lines in 69 files lost coverage.
• Overall coverage increased (+0.04%) to 1.226%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
plugins/csp-atmospheres/src/Atmosphere.cpp	0	1	0.0%
plugins/csp-lod-bodies/src/PlanetShader.cpp	0	1	0.0%
plugins/csp-minimap/src/Plugin.cpp	0	1	0.0%
src/cs-core/GuiManager.cpp	0	1	0.0%
src/cs-core/Settings.cpp	0	1	0.0%
src/cs-graphics/ColorMap.cpp	0	1	0.0%
src/cs-gui/internal/RequestHandler.cpp	0	1	0.0%
src/cs-gui/internal/WebApp.cpp	0	1	0.0%
src/cs-utils/Downloader.cpp	0	1	0.0%
src/cs-utils/filesystem.cpp	11	12	91.67%

Files with Coverage Reduction	New Missed Lines	%
plugins/csl-node-editor/src/Node.hpp	1	0.0%
plugins/csl-tools/src/geometries.cpp	1	0.0%
plugins/csp-atmospheres/src/Atmosphere.cpp	1	0.0%
plugins/csp-atmospheres/src/Plugin.cpp	1	0.0%
plugins/csp-custom-web-ui/src/Plugin.hpp	1	0.0%
plugins/csp-demo-node-editor/src/nodes/DisplayNode.cpp	1	0.0%
plugins/csp-lod-bodies/src/Plugin.hpp	1	0.0%
plugins/csp-lod-bodies/src/TerrainShader.cpp	1	0.0%
plugins/csp-lod-bodies/src/utils.cpp	1	0.0%
plugins/csp-measurement-tools/src/DipStrikeTool.cpp	1	0.0%

Totals
Change from base Build 14053686187:	0.04%
Covered Lines:	208
Relevant Lines:	16971

---

💛 - Coveralls

[Schneegans]

Code-wise it looks good. I'll do some in-depth testing next.

[JonasGilg]

Code-wise it looks good. I'll do some in-depth testing next.

Thanks, this is not an urgent PR (also why this is in draft mode), since we currently have to support Ubuntu 22.04 which doesn't have gcc-13. Maybe in the next months we can drop Ubuntu 22.04 support. But you can review it nonetheless if you have the time.

[Schneegans]

I think everything looks good! Thanks for this work!