feat: Increase reputation on successful loan payment

[Bosun-Josh121]

Pull Request

Description

Integrates reputation score increases on successful loan repayment. Borrowers now receive a score bonus based on payment timing: +15 for early repayment (before the due date) and +10 for on-time/late repayment. Failures in the reputation contract call are handled gracefully and never block a repayment from completing.

Closes #22

Type of Change

• Bug fix
• New feature
• Breaking change
• Documentation update

Changes Made

• Added handle_reputation_increase helper function in CreditLineContract that calculates score increase based on payment timing (payment_date < due_date → +15 early bonus, otherwise +10 on-time)
• Replaced inline full_repayment_reward reputation call in repay_loan with a call to the new helper, using the last installment's due_date as the reference date
• Reputation call uses try_invoke_contract so failures are silently ignored — repayment always succeeds regardless of reputation contract availability
• Updated existing e2e test assertion to reflect early repayment now correctly yields +15 instead of +10

Testing

• Tests pass locally
• New tests added (if applicable)

New tests added in creditline-contract/src/tests.rs using the full RealIntegrationCtx integration setup:

• test_on_time_full_repayment_increases_score_by_10 — payment at exactly the due date gives +10
• test_early_full_repayment_increases_score_by_15 — payment before the due date gives +15
• test_partial_repayment_does_not_change_reputation_score — partial payment triggers no score change
• test_reputation_call_failure_does_not_block_repayment — loan moves to Paid even when the reputation contract rejects the call (updater permission revoked)

Checklist

• Code follows project style guidelines
• Self-review completed
• Comments added for complex code
• Documentation updated
• No new warnings generated