take()/drop(): raise a clear ValueError for negative n

[rantkiglorelgmx-lab]

What

take(n, seq) and drop(n, seq) already reject negative n (via the underlying itertools.islice), but with an opaque message — ValueError: Stop argument for islice() must be None or an integer: 0 <= x <= sys.maxsize. / similar for drop. This adds an explicit guard raising a clear, function-specific message instead:

if n < 0:
    raise ValueError('take: n must be a non-negative integer, got %r' % (n,))

(and the equivalent for drop).

Backward compatibility

Add-only — negative n already raised before this change; only the message is clearer. n == 0 and n >= 1 behavior is completely unchanged (verified: take(0, seq) == [], drop(0, seq) == list(seq), unchanged for all n >= 1).

Note

I noticed #627 already addresses tail(n, seq) for n <= 0 — that fix is out of scope here; this PR only covers take/drop's negative-n error message, which doesn't overlap with it.

Verification

Both commits independently red-before-green verified (100% changed-line coverage, all changed-line mutants caught under AST-level mutation testing). Full suite green: 183 passed, 1 deselected.

Co-authored by Claude (Anthropic) as part of an automated hardening pass; independently re-verified before submission.