bugfix: funding collisions in campaigns

[zeroXbrock]

Motivation

campaigns were panicking in situations where we started multiple spammers because they were all calling fund_accounts with the same accounts, leading to errors like "replacement tx underpriced"

Solution

Call args.init_scenario outside of the "start async spammer" logic in campaigns, so that we wait for funding txs to be confirmed before launching the spammer.

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