Make prune batch size configurable

[mkysel]

Make prune batch size configurable by adding BatchSize field to PruneConfig struct and updating DeleteExpiredEnvelopesBatch function to accept parameterized batch size

Adds a configurable BatchSize field to the PruneConfig struct with a default value of 10000, accessible via --batch-size command line flag and XMTPD_PRUNE_BATCH_SIZE environment variable. The changes include:

• Modifies the DeleteExpiredEnvelopesBatch function in pkg/db/queries/prune.sql.go to accept a batchSize parameter instead of using a hardcoded limit of 1000
• Updates the SQL query in pkg/db/sqlc/prune.sql to use parameterized @batch_size instead of hardcoded LIMIT 1000
• Adds validation in NewPruneExecutor function in pkg/prune/prune.go to ensure BatchSize is greater than 0
• Updates the prune executor to pass the configured BatchSize to the database query

📍Where to Start

Start with the PruneConfig struct in pkg/config/pruneOptions.go to understand the new configuration field, then review the NewPruneExecutor function in pkg/prune/prune.go to see how the configuration is validated and used.

Changes since #964 opened

• Modified test configuration to set fixed batch size [023bf46]

---

Macroscope summarized 023bf46.

[graphite-app]

How to use the Graphite Merge Queue

Add either label to this PR to merge it via the merge queue:

• Queue - adds this PR to the back of the merge queue
• Hotfix - for urgent hot fixes, skip the queue and merge this PR next

You must have a Graphite account in order to use the merge queue. Sign up using this link.

An organization admin has enabled the Graphite Merge Queue in this repository.

Please do not merge from GitHub as this will restart CI on PRs being processed by the merge queue.