feat: Add isValidDomain helper for validation

[iamsivin]

This PR adds a new helper isValidDomain

Returns true for:

• Empty string (treated as valid).
• Standard domains: google.com, example.org, test.net.
• Subdomains (any depth): www.google.com, api.example.org, deep.nested.subdomain.com.
• Hyphens in the middle: my-site.com.
• Multi-part TLDs: example.co.uk, test-domain.co.uk.
• Labels with digits: 123domain.org.
• Internationalized (Unicode) domains: 测试.网络, пример.рф.
• Length limit: total domain length ≤ 253 chars; each label 1–63 chars.

Returns false for:

• Single-label hosts: localhost.
• Invalid characters: example.com!, test@domain.com, spaces, underscores, etc.
• Dot misuse: example..com, ..example.com, example.com...
• Bad hyphen placement: labels starting/ending with -, e.g., -example-.com.
• Too long overall (e.g., 250+.com pushing length >253).
• IP addresses: 192.168.1.1, 127.0.0.1.
• URLs or paths: http://example.com, https://example.com, example.com/path.
• Non-strings / blanks: null, undefined, numbers, objects, arrays, or just spaces.
• Double hyphens anywhere (disallowed by the regex), which also blocks punycode-style xn--… labels.

[github-actions]

size-limit report 📦

Path	Size
dist/utils.cjs.production.min.js	10.93 KB (+47.97% 🔺)
dist/utils.esm.js	10.36 KB (+52.46% 🔺)