Docs: three reference statements disagree with the runtime (reply, constant-time compare, call deadline) #3480

Three statements in the reference documentation disagree with what the code does. Found by the review of PR #3477 (which fixes the same misreadings where the learning path made them) and filed for the next batch.

1. docs/language-reference.md, "Reply Statement" says that omitting reply in a handler invoked with ? makes the caller time out ("ask timed out after 5000 ms"). The runtime ends the ask at once when the handler returns without replying (AETHER_ASK_NO_REPLY, runtime/actors/aether_step_barrier.h, "A handler that took an ask and returned without replying"), with "the handler returned without replying". The error table a few screens up in the same file already says so; the timeout is for a handler that has not returned.

2. docs/stdlib-reference.md, std.cryptography says equality checks are not constant-time and "callers comparing hashes for security-sensitive cases need their own constant-time helper". std.cryptography.ct has one: ct.bytes_eq(a, b, n) and ct.bytes_eq_slice(a, b). The note should point there (examples/03-std/11-cryptography.ae uses bytes_eq_slice for an HMAC tag since One way to learn Aether, and main's red Linux leg: the path, batch 9's examples, a glossary, Rosetta Code, #3432 and #3481 #3477).

3. docs/emit-lib.md, "Per-call resource caps" calls aether_set_call_deadline(50) "50 ms wall-clock" and the knobs per-call. The deadline is one instant per thread, now + ms when it is set (aether_caps_set_deadline_ms, runtime/aether_resource_caps.c), not a budget each call gets: every call made after that instant is cut at its first safe point until the host sets a fresh one or 0. The section should say that, as the header comment in libaether.h nearly does.