Use MassInsertBuilder for PutMessageSecrets, PutManySessions, PutManyLIDMappings

[AlejoGarat]

Problem

PutMessageSecrets, PutManySessions, and PutManyLIDMappings execute one db.Exec per row inside a DoTxn, resulting in N sequential round-trips to the database per call.

This is particularly noticeable during:

• Pairing / initial sync: WhatsApp sends a large batch of message secrets and session keys at once, triggering dozens to hundreds of sequential inserts within a single transaction.
• Mass reconnects: many users reconnecting simultaneously each trigger their own slow transactions, compounding the contention.

The DoTxn slow-transaction monitor (in go.mau.fi/util/dbutil) logs "Transaction still running" every 5s and "Transaction took long" on close for transactions exceeding 1s. These warnings appear frequently.

Solution

Use MassInsertBuilder (already available in go.mau.fi/util/dbutil and already used by PutAllContactNames and PutManyRedactedPhones) to reduce N round-trips to a single bulk INSERT per chunk of 500 rows.

Changes:

• Add GetMassInsertValues() [4]any to MessageSecretInsert (in store/store.go)
• Add GetMassInsertValues() [2]any to addressSessionTuple (in sqlstore/store.go)
• LIDMapping already had GetMassInsertValues(); add the builder and refactor PutManyLIDMappings
• PutManyLIDMappings keeps the per-row DELETE (needed for stale PN→LID cleanup) and batches only the INSERT

Before / After

Before (PutMessageSecrets with 200 inserts):

• 200 × db.Exec(putMsgSecret, ...) inside a single transaction
• 200 sequential round-trips to the database

After:

• 1 × db.Exec with INSERT INTO whatsmeow_message_secrets VALUES ($1,$2,...), ($1,$6,...), ...
• 1 round-trip for up to 500 rows (chunked if more)