migrate parser tests to modern namespaced classes

Move old-style parser tests from _test/tests/inc/parser/ to namespaced
test classes under _test/tests/Parsing/ParserMode/ and
_test/tests/Parsing/Le

migrate parser tests to modern namespaced classes

Move old-style parser tests from _test/tests/inc/parser/ to namespaced
test classes under _test/tests/Parsing/ParserMode/ and
_test/tests/Parsing/Lexer/.

- Add ParserTestBase with assertCalls() helper for comparing handler
call sequences with byte index stripping
- Split lexer.test.php into ParallelRegexTest, StateStackTest, and
LexerTest with a RecordingHandler that extends Handler
- Merge handler_parse_highlight_options tests into CodeTest
- Add new tests for previously untested modes: Nocache, Notoc, Rss,
and all individual formatting modes (Strong, Emphasis, etc.)
- Modernize test code: [] syntax, lowercase null, correct assertEquals
argument order, replace deprecated withConsecutive and string callables
- Renderer tests remain in old location (renderers not yet migrated)

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