feat: add --fee-strategy flag for adaptive fee calculation

[qu0b]

Summary

• Restores the original fee calculation as the default behavior (use provided fees or fetch from network via eth_gasPrice)
• Moves the dynamic headroom + normal distribution fee calculation behind fee_strategy: adaptive
• Fee strategy is per-spammer via WalletPoolConfig, not global — each spammer in daemon mode can use a different strategy
• Keeps the client distribution fix from fix: use baseFee*2 for feeCap and distribute tx submissions across all clients #207 untouched
• Fixes an EIP-1559 violation where feeCap < tipCap could occur in the adaptive strategy due to normal distribution sampling
• Updates all 42 scenario call sites to use walletPool.GetSuggestedFees() (reads strategy from config)

The adaptive strategy uses a sliding window of recent block gas usage to compute dynamic headroom above the average baseFee, with a normal distribution spread across transactions. This creates a self-correcting feedback loop: when blocks are full and baseFee is rising, more transactions land below the current baseFee and get rejected, reducing throughput until baseFee recovers.

Configuration

CLI (single scenario)

spamoor eoatx --fee-strategy adaptive -h http://localhost:8545 -p <privkey>

YAML (per-spammer in spamoor run or daemon mode)

- scenario: eoatx
  name: "adaptive-spammer"
  config:
    fee_strategy: adaptive
    throughput: 50

YAML (mixed strategies — different per spammer)

- scenario: eoatx
  name: "legacy-spammer"
  config:
    throughput: 50

- scenario: eoatx
  name: "adaptive-spammer"
  config:
    fee_strategy: adaptive
    throughput: 50

Daemon mode (via UI/API)

Set fee_strategy: adaptive in the spammer config — each spammer gets its own WalletPool with independent fee strategy.

Kurtosis (spamoor_params)

spamoor_params:
  spammers:
    - scenario: eoatx
      config: {fee_strategy: adaptive, throughput: 50}

Docker

docker run ethpandaops/spamoor:latest eoatx --fee-strategy adaptive -h http://el:8545

Test plan

• Built successfully (go build ./..., go vet ./..., go fmt ./...)
• Tested legacy (default) strategy via CLI in Kurtosis network (geth+reth, lighthouse) — 10 tx/block confirmed
• Tested adaptive strategy via --fee-strategy adaptive CLI flag — 10 tx/block confirmed, zero errors
• Tested adaptive strategy via YAML config fee_strategy: adaptive in spamoor run — 10 tx/block confirmed, zero errors
• Verified client distribution fix from fix: use baseFee*2 for feeCap and distribute tx submissions across all clients #207 is preserved

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