feat: write cache misses with a single setMany

[mvantellingen]

toCache issued a set per cache key and never collected the promises:

for (const [key, value] of items) {
	options.store.set(key, value, options.ttl);
}

Found while looking at a category page trace in a storefront that uses this
through @evolve-framework/commercetools' dataloaders: 35 redis-SET spans in
one request, against 6 redis-MGET — reads batch through store.get(keys),
writes did not. Over two hours redis-SET was the single most-emitted span in
that service (1021 spans, P50 99ms, P95 496ms), which drowned out everything else
in the trace.

What this is not

Not a round-trip win. Measured against a real Redis by patching
net.Socket.prototype.write, 35 keys of ~2KB, three runs:

path	socket writes	all writes dispatched within	complete
for (…) store.set(), not awaited (before)	35	0.2 ms	3.4–3.9 ms
for (…) await store.set() (hypothetical)	35	27 ms	27 ms
store.setMany() (this PR)	36 (MULTI + 35× SET)	0.1 ms	1.6–1.9 ms

The old writes went out within 0.2 ms without waiting for replies, so the client
already pipelined them. Same command count, same bytes (76690 vs 76675).

What it is

• One batch instead of one command per key. @keyv/redis.setMany builds a
  single MULTI/EXEC, so tracing reports one batch span instead of 35.
• The writes are awaited, so a failing store surfaces as an error event on
  it rather than as a floating rejection.

The keyv floor

setMany needs keyv >= 5.3.4; the peer range moves from >=4.0.0 <6.0.0.
Before 5.3.4 Keyv.setMany hands entries straight to the store adapter with no
{value, expires} wrapper, no serialization and no key prefix — so it writes
values get cannot read back, silently. Verified per version:

5.3.3: raw entries    5.3.4: serializes    5.4.0: serializes    5.5.x: serializes

Verification

pnpm test (8 passed) and pnpm check green, plus against a real Redis with
MONITOR attached:

• 8 keys through DataLoaderCache produce one MULTI … 8× SET … EXEC
• a second loader that throws if it reaches the origin serves all 8 from Redis,
  so setMany writes what get parses
• set and setMany land on byte-identical keys, both with a TTL — otherwise a
  release would silently invalidate every cached entry

[changeset-bot]

🦋 Changeset detected

Latest commit: 97f2c75

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@labdigital/dataloader-cache-wrapper	Minor

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