Add portable Authenticode PowerShell cmdlets

[Marc-André Moreau (mamoreau-devolutions)]

Summary

• Adds a portable PowerShell 7.4 / .NET 8 module (Devolutions.Psign) with Get-PortableSignature and Set-PortableSignature backed by the Rust psign_portable shared library through P/Invoke.
• Introduces reusable portable core/FFI crates for signing and inspection across PE, CAB, MSI, ZIP Authenticode, PowerShell scripts/modules, and MSIX/AppX.
• Adds migration-focused cmdlet coverage: content mode, IncludeChain, RFC3161 timestamping, explicit anchor trust policy, portable cert-store thumbprint selection, Force/WhatIf behavior, and rich PortableSignature metadata.
• Adds PowerShell module build/package scripts, CI workflow, docs, and exhaustive module E2E tests.

Validation

• cargo fmt --all --check
• cargo clippy --workspace --all-targets --locked -- -D warnings
• cargo test --workspace --locked
• dotnet build .\dotnet\Devolutions.Psign.PowerShell\Devolutions.Psign.PowerShell.csproj -c Release
• pwsh -NoLogo -NoProfile -File .\PowerShell\tests\Invoke-PortableSignatureTests.ps1 -Configuration Release
• pwsh -NoLogo -NoProfile -File .\PowerShell\package.ps1 -Configuration Release