Introduced the `UnitOfLength` enum to represent measurement units
(Inch and Point) for signature positioning, with detailed
documentation and conversion logic.
Updated `SignatureDto` to use `init` accessors for immutability,
added backing fields for `X` and `Y` with conversion support, and
introduced the `Factor` property to handle unit conversions.
Added a `Convert` method to enable switching between units of
length and improved extensibility for future `SenderAppType`
support. Enhanced code readability and maintainability with
detailed comments and remarks.
TekH
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