[WIP] Update README.md to document all exported members and usage

[Copilot]

Update README.md to document all exported members from the module:

• Analyze current codebase and exported members
• Verify existing tests and build system work correctly
• Update README.md to add documentation for IPv4 class
• Update README.md to add documentation for IPv6 class
• Update README.md to add documentation for IPRange class
• Clarify the distinction between IP utility object and IP type
• Ensure all static vs instance methods are clearly marked
• Test and validate documentation accuracy
• Final review and commit

The goal is to document all exports from src/index.ts including:

• IP (utility object) with static methods parse() and cmp()
• IP (type) representing IPv4 | IPv6 union type
• IPv4 class with static methods (parse, cmp), instance methods (toString, cidr), and version property
• IPv6 class with static methods (parse, cmp), instance methods (toString, cidr), and version property
• IPRange class with static method (parse), instance methods (toString, ips), and properties (first, last, version)

This pull request was created as a result of the following prompt from Copilot chat.

Update the README.md to clearly document all exported members from the module, as exported by src/index.ts (and re-exported by mod.ts), including:

• IP: A utility object for parsing and comparing addresses, with methods IP.parse(string) and IP.cmp(a, b).
• IP (type): The union type representing either an IPv4 or IPv6 address instance.
• IPv4: Class representing an IPv4 address, with static methods (parse, cmp), instance methods (toString, cidr), and version property.
• IPv6: Class representing an IPv6 address, with static methods (parse, cmp), instance methods (toString, cidr), and version property.
• IPRange: Class representing a range of IP addresses, with methods such as toString and ips().

For each export, provide a brief description and minimal usage example, eliding unimportant or trivial code with ... per project conventions. Clarify when a method is static or instance. Ensure the documentation matches the actual exports and their signatures.

Do not include full code snippets; use ... where appropriate. Keep the documentation concise and focused on the actual API surface.

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