AZIP-23: Introduce a Protocol Fee Margin

[aminsammara]

Adds AZIPs/azip-23-protocol-fee-margin.md (category: Economics, status: Draft).

Introduces a governance-set margin μ on the mana base fee. The fee becomes cost × (1 + μ) × congestionMultiplier: operators continue to receive exactly cost from the fee waterfall plus the unchanged block reward, and the markup above cost is paid to a governance-set protocolFeeRecipient, which defaults to the current burn address. The rollup deploys bit-identical to today at μ = 0, after which governance raises μ in rate-limited steps.

Notes for review:

• Requires a rollup redeploy via a governance proposal, since FeeLib/RewardLib are inlined into the rollup bytecode.
• discussions-to is N/A, matching prior Economics AZIPs (e.g. AZIP-16).
• Number 23 is the next free number (highest currently claimed is 22); happy to have the editor reassign.