re-refactor spammer

[zeroXbrock]

Motivation

fully resolves #395

Solution

• run TxActor outside of spam loop, so spammer isn't bound to its lifetime
• purge stale tx hashes from cache in TxActor

PR Checklist

• Added Tests
• Added Documentation
• Ran cargo +nightly clippy --workspace --lib --examples --tests --benches --all-features --locked --fix
• Ran cargo fmt --all
• Note breaking changes in PR description, if applicable
• update changelogs
  • Update CHANGELOG.md in each affected crate
  • add a high-level description in the root changelog