Add Input Validation and Type Safety Improvements

[clcl777]

This PR implements simple input validation and type safety improvements !

• Date validation: Validation to ensure dates are in correct YYYY-MM-DD format and not in the past
• Trip type validation: Validation for trip types against allowed values (round-trip, one-way, multi-city)
• Seat type validation: Validation for seat types against allowed values (economy, premium-economy, business, first)
• Flight data validation: Check to ensure round-trip bookings have at least 2 flight segments
• Fetch mode validation: Validation for fetch modes against allowed values
• Data source validation: Validation for data source parameters

[abhinavm24]

Hey @clcl777 can you please look at https://github.com/AWeirdDev/flights/pull/82/files
Feel free to port your validations to my pr

[abhinavm24]

also, you have to build on dev branch instead of main

[clcl777]

Okay, I see
Plz wait a moment