Fix normalized string append after clear #1636

[Anantha-Kandrapu]

1. Rewrite of the append method:

   • The previous implementation used character indices and transformations.
   • The new implementation directly appends the string and updates alignments.

2. Update to the clear method:

   • Instead of using the transform method, it now directly clears the normalized string and alignments.
   • Adds a single alignment point to represent the empty state after clearing.

3. New test case:

   • Added test_append_after_clear to verify the behavior of appending after clearing a NormalizedString.
   • This test ensures that appending works correctly after clearing, and that original and normalized lengths are maintained properly.

#1636