Optimize and improve request module

[lvitals]

Performance Improvements:

• Cached frequently used functions and methods
• Optimized string operations
• Reduced unnecessary table creations

Code Quality:

• Centralized regex patterns as constants
• Improved error handling
• Added safety checks for edge cases
• Reduced code duplication
• Standardized code formatting

Maintainability:

• Better code organization
• More consistent style
• Clearer separation of concerns

[tomasguisasola]

Have you tested the code? I think I found some mistakes:

1. At line 121, the variable _ in your code is a global, but it was a local in the original;
2. At line 158, you could also use a constant for the pattern (just a suggestion);
3. Also at line 158, you should not use %- when using string.find with true as the fourth value, since it turns off the pattern matching facilities (the same occurs at line 160);
4. At lines 159, 161 and 163, the new call input(length) is not the same as the original wsapi_env.input:read(length), since the first argument (wsapi_env.input) is absent: you might correct that!
5. You also make a different metatable, although with the same content, for each :new call

[lvitals]

Hi @tomasguisasola,

Thank you so much for the detailed and insightful feedback! You've pointed out some very important issues.
I've pushed a new version that addresses all of them.

Here’s a summary of the corrections based on your comments:

• Global Variable (_): You were right about the global _ on line 121. I've fixed this by ensuring the
  variable is properly declared as a local within its scope.

• Pattern Constants and %- Usage: Great suggestion for line 158. I have refactored the code to use
  constants for the content-type strings, which improves readability. I also removed the unnecessary %-
  escaping, as you correctly pointed out that it's not needed when string.find is used with the plain flag.

• input(length) Call: You spotted a critical bug here. This was a major issue that is now fixed. I've
  corrected the logic to ensure wsapi_env.input:read(length) is called as a method, passing the self argument
  correctly.

• Shared Metatables: This was a great catch for performance. I've refactored the request.new function to
  create the metatables for params and cookies only once. They are now shared across all request instances,
  which significantly reduces memory allocation and CPU overhead, especially under high load.

To validate this performance improvement, I've also added a new test file, tests/test_metatable.lua, which
includes a benchmark and an assertion to confirm that the metatables are indeed being shared.

Thanks again for your thorough review! Let me know if you have any other questions or suggestions.