Wire timeout flag to requests

[agourlay]

Wire --timeout into per-request server-side timeouts

--timeout only configured the tonic channel deadline (client-side).

Qdrant aborts long operations using a separate per-request timeout field on the request payload, so against a slow on disk search the server returns a Timeout error before the channel deadline.

Thread args.timeout into every request builder that exposes a server-side .timeout():

• QueryBatchPointsBuilder (main + search-quality exact) in src/search.rs
• ScrollPointsBuilder in src/scroll.rs and src/query.rs
• UpsertPointsBuilder and SetPayloadPointsBuilder in src/upsert.rs

Also added added a fixed 5-second cushion to the channel deadline so the server's structured timeout error reliably wins the race over the transport deadline.

Doc on --timeout updated to reflect the dual scope (channel deadline + server-side request timeout where supported).
Collection-management builders also expose .timeout() but are left untouched for this fix.