[bug] : parseId() and isId() accept IDs with an empty body

[suhailopensource]

Verified on main:

parseId("user_");      // => { prefix: "user", id: "" }
isId("user_", "user"); // => true
getPrefix("user_");    // => "user"

"user_" is a prefix and a separator with no ID after it — it cannot be a value this library
produced, since every generator appends at least one random character. But all three read-side
functions report success, so code that parses an ID and then looks it up gets an empty-string
key instead of a rejection.

Intended semantics — decided, do not re-litigate in the PR

• parseId returns undefined when the body after the separator is empty.
• isId is unchanged — it is documented as a prefix check, and tightening it would break
  callers relying on the current behaviour. Any change there waits for 2.0.
• getPrefix is unchanged for the same reason.

What to do

Add the empty-body guard to parseId in src/utils/validate.ts, alongside the non-string guard
added in #13. Document in the README/docs that parseId is the strict reader and isId is the
loose prefix check.

Acceptance criteria

• parseId("user_") returns undefined; parseId("user_x") still returns
  { prefix: "user", id: "x" }.
• Same behaviour with a custom separator: parseId("user.", ".") is undefined.
• isId and getPrefix behaviour is untouched, with a test asserting isId("user_", "user")
  is still true so the distinction is pinned.
• Tests in test/validate.test.ts; CHANGELOG entry under Unreleased (this is a user-visible
  behaviour change).
• No inline comments — see CONTRIBUTING.

[Nityam43]

I would like to work on this!

[suhailopensource]

@Nityam43 sure . Do star the Repository . Thanks