Add maximum repo string and title length validation - #1137

Closes #759

Description

Type of change

• Bug fix
• New feature
• Breaking change

Security Checklist

Please review the SECURITY_CHECKLIST.md and check off any items that apply. Reviewers must sign off on these items before merge.

• Input validation changed
• Auth modified
• New external fetch
• Dependency added
• Secret handling

Title: Add maximum repo/title length tests for create_bounty

Summary:
Adds unit tests that validate repo and title length handling in the contracts package. Tests cover at-limit acceptance, over-limit rejection (returns StringTooLong), and empty-string acceptance.

Branch: AddMaximumRepoStringAndTitleLengthValidation

Files Changed:

• Tests: test.rs

What I changed:

• Added three tests to validate string length behavior for create_bounty:
  • At-limit: repo and title exactly at MAX_REPO_LEN / MAX_TITLE_LEN are accepted.
  • Over-limit: repo one char longer than MAX_REPO_LEN fails with StringTooLong.
  • Empty: empty repo/title strings are accepted.

Rationale:
Protects on-chain storage from unbounded growth by ensuring length limits are enforced and prevents regressions by asserting expected contract behavior.

Testing:

• Run the contracts test suite:
  • cargo test -p contracts
• To run only the new tests (example):
  • cargo test -p contracts test_create_bounty_repo_title_at_limit_succeeds
  • cargo test -p contracts test_create_bounty_repo_over_limit_fails
  • cargo test -p contracts test_create_bounty_empty_repo_title_succeeds

Expected Results:

• Tests pass if create_bounty enforces MAX_REPO_LEN / MAX_TITLE_LEN and returns StringTooLong on over-limit inputs.
• Behavior for valid-length bounties is unchanged.

Notes / Caveats:

• These are unit tests only and do not modify contract runtime logic — they assert existing behavior implemented in lib.rs.
• The over-limit test expects the contract to surface the StringTooLong error (the test uses #[should_panic(expected = "StringTooLong")]).

Checklist for PR:

• Behavior: Tests added and passing locally.
• CI: Ensure cargo test -p contracts runs in CI.
• Reviewers: Contracts maintainers / reviewers familiar with Soroban SDK and on-chain storage constraints.

Suggested PR description (copy-paste):

Adds unit tests to validate repo/title string length handling in the Soroban contract.

• Adds tests for:
  • repo/title at exact allowed length (should succeed)
  • repo over the limit (should fail with StringTooLong)
  • empty repo/title (should succeed)

This prevents regressions around string-length validation that protects on-chain storage. Tests live in test.rs on branch AddMaximumRepoStringAndTitleLengthValidation. Run cargo test -p contracts to verify.