add processing imported ratelimit configs

[m2broth]

Summary
Enhance initializer resolver to evaluate decorator arguments passed as named-imported consts by following import aliases to their exported declarations.
Simplify supported expression kinds and align fixtures/tests with the intended scope.

Motivation
Previously, when a decorator argument was a named import, the resolver saw only the alias symbol at the call site and failed to resolve it to the exported declaration.

This broke cases like:

import { userIpRateLimitConfigExpr } from './rateLimitConfigs'

@RateLimitByUserIp(userIpRateLimitConfigExpr)

What's Changed

• Added alias resolution for ImportSpecifier:
• Introduced getImportSpecifierValue(importSpecifier, typeChecker).
• Uses typeChecker.getAliasedSymbol to find the exported declaration and evaluate its initializer.
• Correctly computes expressions like 15 * 60 in configs:
  export const rateLimitConfig = { limit: 100, slidingWindowSec: 15 * 60, }