AZIP-25: Activity Score for Full Epoch Proofs

[aminsammara]

Adds AZIPs/azip-25-full-epoch-proof-activity-score.md (category: Core, status: Draft).

Restricts the prover activity score increment to proofs that cover a complete epoch. Today RewardLib.handleRewardsAndFees calls updateAndGetShares for every accepted proof, the increment does not depend on proof length, and the protocol accepts a proof of a single checkpoint. A prover that cannot keep up with a congested epoch can therefore hold its score by proving one checkpoint, then collect a full reward share on a later, cheaper epoch. This AZIP gates the increment on a full epoch proof — the same condition that already gates reward eligibility. Fees, reward totals, and proof validity rules are unchanged.

Notes for review:

• Requires a rollup redeploy via a governance proposal, since EpochProofLib and RewardLib are internal libraries inlined into the Rollup bytecode; this cannot ship as a config change.
• The Specification adds a proofSubmissionEpochs > 0 constructor requirement. Without it no full epoch proof can exist and the mechanism becomes dead code with no error; the reference PR notes the hazard in a comment but does not yet enforce it.
• discussions-to is N/A, matching prior AZIPs (e.g. AZIP-23, AZIP-16).
• Number 25 is the next free number after AZIP-24; happy to have the editor reassign.