feat: coin issuer uses percentage of total supply

[just-mitch]

Redesign CoinIssuer to use annual percentage-based minting budgets

This PR redesigns the CoinIssuer contract to implement a more sophisticated token issuance model:

• Replaces the continuous rate-based minting with a discrete annual budget system
• Budgets are calculated as a percentage of total supply at the start of each year
• Implements a "use-it-or-lose-it" model where unused budget is lost when crossing year boundaries
• Enables proper compounding as each year's budget is based on the actual supply at that time
• Sets a hard cap of 20% annual inflation in the deployment script

The implementation includes:

• New state variables to track current year, budget, and cumulative minted amount
• Logic to handle year boundary transitions and budget recalculation
• Comprehensive test coverage for various scenarios including partial minting, year transitions, and skipping years

This approach provides more predictable token issuance with clear annual caps while still allowing flexibility in the actual minting schedule within each year.

[just-mitch]

• feat: coin issuer uses percentage of total supply #17738 👈 (View in Graphite)
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[LHerskind]

Updated to keep is slightly more limited in extra storage and to better reuse functions. Would prefer another pair of eyes since I made those changes.

[AztecBot]

✅ Successfully cherry-picked 1 commit(s) to backport staging branch backport-to-v2-staging.