redis_boolean_response and redis_long_response read the reply with
redis_sock_read, which estrndup's the +OK / :N line onto the heap, then
inspect only the first byte (or parse the integer) and efree it. Every
SET, INCR, EXPIRE, SADD, DEL, EXISTS and similar command paid a wasted
allocation.

Extract the shared dispatch into redis_sock_read_into, which writes a
single-line reply into a caller-provided buffer (borrowed, no heap) and
only heap-allocates for bulk bodies. redis_sock_read becomes a thin
wrapper that estrndup's the borrowed line so its existing callers are
unaffected. The two handlers now read into a stack buffer and only free
when the reply was an (unexpected) bulk, which the shared reader still
drains so the stream stays in sync.

Verified on PHP 8.4: status/integer responses (incr/decr/zero/negative,
near INT64_MAX, +OK booleans, :1/:0, error replies via the '-' path),
bulk path unchanged through the wrapper, no leaks under report_memleaks,
and testSetGet/testIncr/testExpire/testExists/testRename/testDel/
testHashes/testKeys.