add Support for Dynamic Library Product in Swift Package, Fixes #595

[kikiwora]

Description

This PR adds support for dynamic linking by introducing a new library product SkeletonView-Dynamic in the Swift Package Manager configuration,
while maintaining the existing static library for backward compatibility.

Changes

• Added a new .library product named SkeletonView-Dynamic with explicit type: .dynamic
• The new product targets the same SkeletonView module as the existing static library
• Maintains backward compatibility - the original SkeletonView library product remains unchanged

Benefits

• Allows consumers to choose between static (default) and dynamic linking
• Useful for scenarios requiring dynamic frameworks (e.g., certain app extensions, reducing binary size with shared frameworks)
• No breaking changes to existing integrations

Usage

Users can now specify the dynamic variant in their Package.swift:

dependencies: [
    .package(url: "https://github.com/Juanpe/SkeletonView.git", from: "1.0.0")
],
targets: [
    .target(
        name: "MyApp",
        dependencies: [
            .product(name: "SkeletonView-Dynamic", package: "SkeletonView")
        ]
    )
]

Testing

• Package validates successfully with swift package dump-package
• Both static and dynamic products are properly configured
• No impact on existing integrations