Fix statement splitting after whitespace-varied compound closers

[AryanRG]

Compound block closing keywords such as END IF and END LOOP can contain repeated spaces, tabs, or line breaks. The lexer recognizes those spellings, but the statement splitter compares their raw whitespace against single-space keywords. It then leaves the block open and merges later statements.

Normalize only the keyword value used for splitter comparisons. The original token text is unchanged. Add regression coverage for five closer types, four separators, anonymous and procedure blocks, and two following statements; update the development changelog.

Validation:

• New regression cases on pristine master: 30 failed, 10 single-space controls passed.
• With this change: all 40 regression cases passed.
• Full tests on Python 3.10, 3.11, and 3.14: 546 passed, 2 expected failures, 1 existing non-strict unexpected pass on each.
• Ruff and diff checks passed.

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