feat: harden NIP-05 validator HTTP handling

[tcheeric]

Summary

• add reusable HTTP client provider with configurable timeouts
• validate and normalize NIP-05 inputs and build URIs safely
• cover validator success, mismatched keys, and network errors with unit tests

Testing

• ❌ mvn -q verify (integration tests failed: Could not find a valid Docker environment)

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https://chatgpt.com/codex/tasks/task_b_68a732cc4a18833192c6f56eebd8a6c0

[codecov-commenter]

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Codecov Report

❌ Patch coverage is 58.33333% with 25 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
...main/java/nostr/util/validator/Nip05Validator.java	56.86%	16 Missing and 6 partials ⚠️
...ava/nostr/util/http/DefaultHttpClientProvider.java	25.00%	3 Missing ⚠️

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