feat: add explicit none aliases and guard refinements

[rustpls]

Summary

• Add explicit isNoneOr... and isNotNoneOr... aliases for empty and whitespace helpers
• Make isNone and isSome type predicates
• Make reverse(array) return a reversed copy instead of mutating the input
• Bump package version from 2.0.0 to 2.1.0
• Fix the README sample to use isNoneOrWhitespace and document the None-safe alias naming

Verification

• deno fmt README.md
• deno fmt deno.json
• deno fmt src/core.ts src/core_test.ts src/strings.ts src/strings_test.ts README.md
• deno test src/core_test.ts src/strings_test.ts
• deno check mod.ts