Upgrade project files to SDK-style format compatible with dotnet

[adecler]

Issues addressed by this PR

Fixes #251

• The project files were still using the legacy .NET Framework project files and needed to be upgraded to SDK-style format compatible with dotnet.
• I have not upgraded the framework to netstandard2.0 as I was not confident this would be compatible for this repo and its dependencies.
• I had to upgrade some nuget package references for the project to compile correctly
• Fix the projects to make sure the compilation output is written directly in the Build folder (not in Build\net472).
• Finally, I have fixed compilation errors due to missing explicit casting of Excel objects.

You can find more details on the logic behind the modifications done in this PR here:
SDK_Migration_Notes.md

Tests

• Make sure the solution build with dotnet build

• Run your end of milestone testing procedure

• There is also an installer for this PR available on SharePoint at BHoM\Excel_UI\#428-UpgradeProjectFormat. You can use it to test this PR but still make sure that dotnet build runs successfully.

Note on the need for explicit casting

The old .csproj explicitly set EmbedInteropTypes=True on the interop reference (confirmed in git). With the old project format (non-SDK, packages.config), the .NET Framework build toolchain's NoPIA (No Primary Interop Assembly) embedding mechanism was more permissive — it allowed implicit assignment from object to a COM interface type that was simultaneously being embedded into the consuming assembly, treating it as type-equivalent at the point of use. The compiler silently inserted the conversion.
The new SDK-style project format uses a stricter Roslyn integration. Even when EmbedInteropTypes=True is active (the default for Interop.* packages), it no longer permits that implicit object → specific COM interface coercion. It requires the cast to be written explicitly.

[adecler]

@BHoMBot check compliance

[bhombot-ci]

@adecler to confirm, the following actions are now queued:

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[adecler]

@BHoMBot check compliance

[bhombot-ci]

@adecler to confirm, the following actions are now queued:

• check code-compliance
• check documentation-compliance
• check project-compliance
• check branch-compliance
• check dataset-compliance
• check copyright-compliance

[adecler]

@BHoMBot check installer

[bhombot-ci]

@adecler to confirm, the following actions are now queued:

• check installer

[adecler]

@BHoMBot check compliance

[bhombot-ci]

@adecler to confirm, the following actions are now queued:

• check code-compliance
• check documentation-compliance
• check project-compliance
• check branch-compliance
• check dataset-compliance
• check copyright-compliance

[adecler]

@BHoMBot check installer

[bhombot-ci]

@adecler to confirm, the following actions are now queued:

• check installer