feat: implement extend_campaign_deadline (#81)

[EDOHWARES]

Overview

This PR implements the `extend_campaign_deadline` functionality, allowing campaign creators to extend their fundraising deadlines if they haven't met their goal yet, while enforcing a maximum extension duration of 90 days.

Implementation Details

• Added `extend_campaign_deadline` to `CrowdfundingTrait` and implemented it in `CrowdfundingContract`.
• Enforced Security Restrictions:
  • Requires original creator's signature (`require_auth`).
  • Rejects extensions if the campaign has already reached its funding goal.
  • Limits the extension to a maximum duration of 90 days from the current timestamp.
  • Ensures the new deadline is explicitly further than the previous deadline.
• Added Test Infrastructure:
  • ✅ `test_extend_campaign_deadline`: Ensures successful updates.
  • ✅ `test_extend_campaign_too_long`: Ensures validation against extensions exceeding 90 days.
  • ✅ `test_extend_campaign_deadline_invalid_auth`: Simulates rejecting operations from malice or impersonation.

Closes #81

[EDOHWARES]

@Akshola00 , pls review

[Akshola00]

@EDOHWARES thankd for your contribution, please resolve conflicts

[EDOHWARES]

@Akshola00 , conflicts resolved

[Akshola00]

lgtm, thanks for your contribution