refactor(proxy): improve proxy factory implementation with lazy loading

[Vincentdevreede]

This PR refactors the proxy factory to lazy-load and cache module imports on first use, and introduces a safe default for missing proxy configuration.

Changes

• Deferred require() calls for fast-proxy-lite, http-lambda-proxy, and fast-proxy until their branch is invoked
• Cached each imported module in the closure to prevent redundant loads
• Added route.proxyConfig || {} fallback
• Replaced the if/else if/else proxyType checks with a switch(proxyType)

No functional changes—internal refactor only.

[jkyberneees]

The PR contain linting issues, please fix accordingly.