fix: detect __DATA__/__END__ and no Module; terminators in source filters

[fglock]

Summary

Improves source filter handling to detect terminator patterns and stop filtering at the appropriate point.

Problem

When applying source filters, Filter::Simple uses terminators like __DATA__, __END__, and no Module; to mark where filtering should stop. Without proper terminator detection:

• Content after __DATA__/__END__ was being lost or filtered incorrectly
• Code after no Module; was being filtered when it should pass through unchanged

Solution

After each filter chunk, check if the output ends with a terminator pattern:

• __DATA__ or __END__ at end of line
• no ModuleName; at start of line (with optional comment)

When a terminator is detected, append the remaining source unchanged instead of continuing to filter.

Test Results

Filter::Simple tests:

Test	Before	After
t/data.t	❌ 3/6	✅ 6/6
t/filter.t	❌ 5/6	✅ 6/6
t/code_no_comments.t	✅	✅
t/export.t	✅	✅
t/import.t	✅	✅
t/filter_only.t	❌	❌ (pre-existing POD bug)

Note: t/filter_only.t fails due to a separate PerlOnJava bug where content between =end formatname and =cut is not treated as POD.

Test Plan

• make - all unit tests pass
• Filter::Simple t/data.t - passes
• Filter::Simple t/filter.t - passes
• Log::Log4perl t/049Unhide.t - still passes

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