Preserve trailing whitespace after the final semicolon

[itzzdev09]

sqlparse.parse() drops a trailing whitespace run that follows the final ; when that run contains a newline, breaking the parse → str round-trip:

>>> import sqlparse
>>> "".join(str(s) for s in sqlparse.parse("SELECT 1;\n"))
'SELECT 1;'          # the "\n" is gone
>>> "".join(str(s) for s in sqlparse.parse("SELECT 1;\t"))
'SELECT 1;\t'        # a tab is kept, so the two disagree

Cause

In StatementSplitter.process, a ; sets consume_ws = True. A following newline is deliberately treated as not whitespace (so the next statement starts at the newline), so it triggers a split and begins a fresh statement. When nothing but whitespace follows to end-of-input, that fresh statement is whitespace-only, and the final guard

if self.tokens and not all(t.is_whitespace for t in self.tokens):

discards it — taking the newline with it. A trailing tab or spaces stays in EOS_TTYPE, so it never splits and is preserved; only newlines are lost, which is why the two cases disagree.

Fix

Hold the previous statement back by one step, and at end-of-input re-attach a final whitespace-only run to it instead of dropping it. Whitespace-only input (parse(" ")) still yields no statements, and statement counts for every existing case are unchanged.

Added test_split_trailing_whitespace_preserved (round-trip for trailing spaces/tabs/newlines) and test_split_whitespace_only; the newline cases fail on master. Full suite passes (506).