Perf: Optimize string concatenation across multiple files

[mohasarc]

This PR optimizes string construction in directive.py, process.py, and event.py by replacing repeated += concatenation inside loops with list accumulation and ''.join().

The Issue: In Python, strings are immutable. Using += to append to a string inside a loop forces the interpreter to create a new string object and copy the old content for every iteration. This results in quadratic time complexity O(n^2), which can significantly degrade performance when processing large inputs.

The Solution: I refactored the string construction logic to collect substrings in a list and use ''.join() at the end. This approach ensures linear time complexity O(n) because the total size of the final string is calculated once, and memory is allocated efficiently.

This is in line with standard python performance recommendation: https://peps.python.org/pep-0008/#programming-recommendations

[mondeja]

Tested locally and it's ~4% faster. Thank you!

[mohasarc]

Glad to hear that :)