[tests] unbond/claim zero

[drew-u410]

Describe your changes

• Additional tests to show reward history wipe after unbond + claim.

$ cargo test test_protocol_bug_fully_unbonded_rewards_history_lost -q -- --nocapture
...
🐛 TESTING PROTOCOL BUG: Fully unbonded accounts lose reward history
========================================================================
✅ STEP 1: Delegator bonded 500.000000 tokens to validator
✅ STEP 2: Accumulated rewards: 4.500000 tokens
✅ STEP 3: Fully unbonded all tokens (remaining bonds: 0.000000)
✅ STEP 4: Rewards after unbond: 4.500000 tokens (preserved in counter)
   📊 Rewards counter before claim: 4.500000 tokens
✅ STEP 5: Claimed rewards: 4.500000 tokens
❌ BUG REVEALED: Rewards counter after claim: 0.000000 tokens
❌ BUG REVEALED: Available rewards after claim: 0.000000 tokens
❌ BUG CONFIRMED: Rewards next epoch: 0.000000 tokens
❌ BUG CONFIRMED: Rewards counter next epoch: 0.000000 tokens

🔍 ANALYSIS:
   Before claiming: 4.500000 tokens available
   After claiming:  4.500000 tokens claimed
   Counter deleted: 0.000000 tokens remain
   Next query:     0.000000 tokens available

🚨 PROTOCOL BUG IDENTIFIED:
   When a fully unbonded account claims rewards, the rewards counter
   is PERMANENTLY DELETED from storage. This means:
   1. The network forgets this account ever earned rewards
   2. Historical reward data is irretrievably lost
   3. Future queries will always return 0
   4. This creates unfair incentives against full unbonding

💡 EXPECTED BEHAVIOR:
   The rewards counter should either:
   1. Be preserved (set to 0) but not deleted, OR
   2. Have separate functions for querying vs claiming
   This would maintain reward history for accounting purposes.

🔄 COMPARISON: Partially unbonded account behavior
   📊 Partial unbond - rewards before claim: 0.000000
   📊 Partial unbond - rewards claimed: 0.000000
   📊 Partial unbond - rewards after claim: 0.000000
   ✅ Partially unbonded accounts can continue earning rewards

========================================================================
🐛 PROTOCOL BUG TEST COMPLETED - Issue clearly demonstrated

Checklist before merging

• If this PR has some consensus breaking changes, I added the corresponding breaking:: labels
  • This will require 2 reviewers to approve the changes
• If this PR requires changes to the docs or specs, a corresponding PR is opened in the namada-docs repo
  • Relevant PR if applies:
• If this PR affects services such as namada-indexer or namada-masp-indexer, a corresponding PR is opened in that repo
  • Relevant PR if applies: