QEarn: Make early unlocks principal-only full exits

[jtskxx]

This PR fixes QEarn early-unlock fairness.

Changes:

• Sets all early-unlock reward percentages to 0.
• Sets all early-unlock burn percentages to 0.
• Makes any post-lock-epoch early unlock exit the full position for that lock epoch.
• Keeps forfeited bonus in the round for remaining 52-epoch lockers.
• Adds a regression test proving early unlockers receive principal only and cannot leave a small remainder to capture boosted rewards.

QEarn computor donations are intended to reward users who complete the 52-epoch lock period. The current early-unlock logic allows short-term lockers to extract or burn part of the shared bonus pool, reducing rewards for loyal long-term lockers. This patch keeps early liquidity available while ensuring bonus rewards belong to completed locks.

[cyber-pc]

@jtskxx You need to set the target branch as qubic:develop not the main branch.

[jtskxx]

Updated the PR so the new QEarn rules are prospective only.

The new behavior is scoped by lockedEpoch:

• locks created before epoch 221 keep their original QEarn terms;
• locks created from epoch 221 onward use the new early-unlock fairness rules.

This addresses the concern that existing lockers should not have their terms changed mid-lock, while keeping the proposal goal unchanged.

[jtskxx]

Updated the PR to prevent same-epoch unlocks for new post-activation locks.

This closes the case where someone could lock a large amount during an epoch, affect the round APY, then unlock before the epoch closes.

Scope remains prospective:

• pre-activation locks keep existing behavior;
• post-activation locks cannot unlock in their lock epoch;
• post-activation early unlocks after that are full-exit and principal-only.