fix: support scalar projection adaptations

[ycherkes]

Summary

• Allow [Adapt] templates returning an unchanged scalar result type, such as bool predicates and int
  projections.
• Preserve destination-construction validation when an adaptation changes the return type.
• Add regression coverage for an adapted nested scalar predicate.
• Bump AlephMapper from 0.7.1 to 0.7.2.
• Update README package references and generated-code baselines.

Validation

• dotnet build tests/AlephMapper.Tests/AlephMapper.Tests.csproj --no-restore
• dotnet tests/AlephMapper.Tests/bin/Debug/net10.0/AlephMapper.Tests.dll --no-ansi --progress off --maximum-parallel- tests 1
• 62 tests passed.