Updated ROADMAP.md to reflect progress on the TDD process for
DevExpressPdfProcessor, including the creation of unit tests
(6 tests in the Red Phase). Updated progress to 4/7 mini-steps
completed and outlined the next step (Green Phase).
Added `DevExpressPdfProcessorTests.cs` with unit tests to
validate PDF files and extract metadata. Tests cover valid
PDFs, null/empty inputs, corrupted PDFs, and file size
calculations. Used `FluentAssertions` for assertions.
Cleaned up `DocumentOperator.Tests.csproj` by removing an
unused folder reference. No functional changes to the project
structure.
