Decode the Slanted Ciphertext

You’re given encodedText produced by writing originalText into a matrix with a fixed number of rows, filling diagonally (top-left → bottom-right), padding remaining cells with spaces, choosing cols so the last column isn’t empty, then reading the matrix row-wise to form encodedText.
Given encodedText and rows, return the unique originalText (with no trailing spaces).

Decoding idea:

• Let cols = len(encodedText) // rows.

• Recreate the rows × cols matrix by filling it row-wise from encodedText.

• Read back along diagonals: for each column c from 0..cols-1, take cells (r, c+r) for r = 0..rows-1 while c+r < cols.

• Join and rstrip() to remove trailing spaces.