Add Stellar security detector rules for upgrade guards, symbol usage, access control, and cross-contract invocation

[bellabuks]

Summary

This PR adds four new static analysis detector rules under targeting common Soroban smart contract security and optimization issues.

Changes

• rules/stellar/upgradeability/detect-missing-upgrade-guards.ts - Detects upgrade functions (, , ) that lack an admin authorization check, flagging contracts vulnerable to malicious upgrades.
• rules/stellar/optimization/detect-inefficient-symbol-usage.ts - Detects repeated inline construction with the same name, suggesting static references to reduce execution overhead.
• rules/stellar/access-control/detect-missing-access-control.ts - Detects privileged functions (, , , , etc.) that are missing a or equivalent role guard.
• rules/stellar/cross-contract/detect-unsafe-cross-contract-invocation.ts - Detects cross-contract invocations (, , etc.) that lack caller validation or result verification.

closes #373
closes #374
closes #375
closes #378

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