SCCP-268: Update staking liquidation parameters

This SCCP proposes the following parameter adjustments:

• Reduce liquidationPenalty to 75% from 60%
• Reduce selfLiquidationPenalty to 70% from 50%
• Reduce liquidationRatio from 175% to 160%
• Reduce liquidationEscrowDuration to 6 months from 12 months

See the SCCP here for discussion of motivation and rationale: https://sips.synthetix.io/sccp/sccp-268