Added enums `PdfSignatureCoordinateUnit` and `PdfSignatureCoordinateOrigin` to support defining signature coordinates in points or inches and relative to either the bottom-left or top-left corner of the page.
Updated `PdfSignatureAppearanceDto` to include `CoordinateUnit` and `CoordinateOrigin` parameters with default values. Refactored `PdfDigitalSignatureService` to use a new `BuildSignatureBounds` method for calculating signature bounds, which handles unit conversion, origin adjustments, and validation.
Introduced `GetPageHeightInPoints` to retrieve page height for top-left origin calculations. Improved signature field naming precision and added error handling for invalid dimensions and page numbers.
Included a TODO for optimizing the signature check algorithm.
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