feat: add is-alphanumerical replacement

[Haasini-kudala]

🔗 Linked issue

Resolves #1001.

📚 Description

Add is-alphanumerical to the micro-utilities manifest with an inline ASCII range check. Like the package, the snippet accepts a numeric character code or checks the first character of a string, and returns false for empty strings and non-ASCII characters.

This follows the existing is-decimal replacement. Comparing the numeric code directly avoids the wrapping and truncation introduced by String.fromCharCode in the issue's suggested snippet. The mapping belongs in micro-utilities because the replacement is a small inline function.

Validation on Node 24:

• pnpm build and pnpm lint passed.
• node scripts/validate-pr.ts passed.
• Compared the manifest's exact snippet against is-alphanumerical@2.0.1 for every Unicode code point as both a number and a string, plus empty/multicharacter strings, numeric boundaries, fractions, and non-finite values: no mismatches.