fix: align testnet slashing penalties with L1 slash amounts

[AztecBot]

Summary

Testnet validators were detecting inactive validators and starting slashing rounds, but all votes were computed as zero because the per-offense penalty (10e18 = 10 TST) was far below the L1 contract's minimum slash threshold (100000e18 = 100,000 TST).

This PR sets all testnet slashing penalty values to 100000e18 to match AZTEC_SLASH_AMOUNT_SMALL, which is the minimum amount needed for a vote to register as 1 slash unit.

Root Cause

The vote computation in getSlashUnitsForAmount() (yarn-project/stdlib/src/slashing/tally.ts) checks if the accumulated offense amount reaches slashingAmounts[0] (= AZTEC_SLASH_AMOUNT_SMALL). Since 10e18 < 100000e18, the function always returned 0 slash units, causing all votes to be skipped.

BigInt Parsing Verification

• The penalty values flow through env vars as strings (e.g. "100000e18")
• bigintConfigHelper in foundation/src/config/index.ts handles scientific notation losslessly using bigint arithmetic (not float64)
• The parsing regex correctly handles 100000e18 → BigInt("100000") * 10n ** 18n = exact result

Changes

• spartan/environments/network-defaults.yml: Updated all testnet SLASH_*_PENALTY values from 10e18 to 100000e18

ClaudeBox log: https://claudebox.work/s/a2a0d7830a3d8ce3?run=2