Batch sender fixed

[stpatrickghost]

Summary

Batch-sender was emitting single-topic ANNOUNCE events, which broke
server-side topic-3 view-tag filtering and forced indexers to full-scan
its output. Per-transfer announcements now go through the announcer
contract, the same announcer_client::announce pattern splitter already
uses, so all three sources emit the v2 4-topic layout:

topics: ("announce", scheme_id, view_tag_bucket, metadata_kind)
data: (stealth_address, ephemeral_pub_key, metadata)

view_tag_bucket = metadata[0] as u32.

Issue #62 is an audit-doc correction only. splitter fund_split already
routes through the announcer; no splitter logic change.

Changes

• stealth-batch-sender: drop inline (ANNOUNCE,) publish; call announcer
  instead. batch_send now takes announcer + scheme_id. Transfer gains
  metadata and uses BytesN<32> for the ephemeral key.
• Unit + snapshot tests assert the 4-topic layout and view-tag derivation.
• New integration test topic_filter.rs: topic-3 filter returns only the
  matching view-tag subset across announcer, splitter, and batch-sender.
• EVENT_INDEXING_AUDIT.md: close Per-network deployment config validation #63 as resolved; close Independent third-party audit preparation pack #62 as a stale
  audit-doc finding.
• Reference indexer processor: one announcement path for announcer,
  sender, splitter, and batch-sender. No batch-sender-specific
  single-topic handler.
• bench-crossover and Cargo.toml/lock updated for the new API.
• stealth-splitter Cargo.toml adds rlib so the integration test can
  link it. No splitter source change.

Test plan

• cargo test -p stealth-batch-sender
• cargo test -p integration-tests --test topic_filter
• cargo check -p stealth-batch-sender -p integration-tests -p stealth-splitter -p wraith-stellar-bench-crossover
• cargo fmt --all -- --check

Closes #159

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[truthixify]

Thanks @stpatrickghost. The stellar job is red on cargo fmt --all --check, not on a test. Four files have formatting drift:

• stellar/bench-crossover/src/crossover.rs:247
• stellar/integration-tests/tests/topic_filter.rs:263
• stellar/stealth-batch-sender/src/lib.rs:164
• stellar/stealth-batch-sender/src/test.rs:387

Fix:

cd stellar
cargo fmt --all
git commit -am "style: cargo fmt"
git push

Everything else in the run is green, including the bench jobs, so this should be the only thing between it and a merge.