Add regression test for governance poll vote weight updating correctly when voter changes their vote

[Chucks1093]

Summary

A holder who changes their vote before a poll expires must have their weight removed from the previous option and added to the new one. A regression test should confirm the tally is updated correctly without double-counting.

Scope

• Create a poll with two options
• Wallet A votes for option 0 with a balance of 10 keys
• Wallet A changes their vote to option 1
• Assert option 0 tally decreased by 10 and option 1 tally increased by 10
• Assert total vote weight across all options remains unchanged

Acceptance Criteria

• Option 0 tally decremented after vote change
• Option 1 tally incremented after vote change
• Total vote weight unchanged after the change
• No double-counting of the voter's weight

ETA: 12 hours

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Coordinate on Telegram

[OluRemiFour]

Hi Maintainer,
Interested in working on this issue. I'll implement the requested changes and ensure everything is properly tested before submission.

[Fury03]

Hi Maintainer I've gone through this and I have a clear implementation plan to execute.
Kindly assign so I can work on this.

[Menjay7]

Hi! I came across this issue and would love to work on it. I have experience with similar tasks and I'm confident I can investigate, implement a clean solution, and thoroughly test it before submitting a PR. If the issue is still open, I would appreciate it if you could assign it to me. Thank you!

[grantfox-oss]

🦊 GrantFox — @Fury03 has been assigned to this issue as part of the Official Campaign | FWC26 campaign!

Next steps:

1. Open a Pull Request referencing this issue (e.g., Closes #539)
2. Your PR will be reviewed by the accesslayerorg maintainers

Good luck! Track your progress on GrantFox.

[grantfox-oss]

🎉 This issue has been marked as completed on GrantFox as part of the Official Campaign | FWC26 campaign!

@Fury03's PR #566 was approved and merged by @Chucks1093.

🏆 @Fury03: You earned 35 FoxPoints for this contribution! Your current tier: Explorer (901 total points). Track your full progress on GrantFox.

👏 Great work, @Fury03! Keep contributing to accesslayerorg.