fix: fetch DripGovernor::config once per batch in create_batch_streams

[mysteriousskater]

Overview

This PR removes the redundant per-stream DripGovernor::config cross-contract calls in create_batch_streams. Instead of letting each stream in a batch independently fetch the same governor config, the batch path now fetches the config once and threads it through an internal helper.

The public create_stream path is preserved and still fetches its own config, so single-stream callers retain existing behavior.

Related Issue

Changes

⚙️ Batch Config Fetch

• [MODIFY] contracts/factory/src/lib.rs
  • Split create_stream into a public wrapper that fetches GovernorConfig via governance::config and delegates stream creation to a new internal helper.
  • Add create_stream_with_config(&config, ...) so both the single-stream and batch paths share the same bounds enforcement and stream creation logic.
  • Update create_batch_streams to fetch the DripGovernor::config once before the stream loop and pass &config into create_stream_with_config for each stream in the batch.
  • Keep the public create_stream behavior unchanged for single-stream callers.

Verification Results

cargo test --package factory
✅ all tests passed

Live acceptance check:
✅ 1 DripGovernor::config cross-contract call per 10-stream batch
✅ create_stream single-stream path still fetches config independently
✅ create_batch_streams preserves all existing stream / batch boundary checks

Acceptance Criteria	Status
create_batch_streams fetches DripGovernor::config once per batch	✅ One config call for the entire batch instead of one per stream
Public create_stream still fetches config for the single-stream path	✅ Public wrapper fetches config internally and delegates to helper
Bounds enforcement still runs for every stream	✅ create_stream_with_config calls enforce_bounds for each stream
Batch host-call overhead is reduced	✅ N cross-contract config calls reduced to 1 for MAX_BATCH_SIZE = 10

Closes #422

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