fix(regex): \cX inside character class consumes next char even if special

[fglock]

Summary

Fixes the regex preprocessor's handling of \cX inside character classes when X is a regex-significant character (], \, [, ^, etc.).

In Perl, \cX is a control-character escape that always consumes the next source character, regardless of what it is — so \c] is U+001D (control-]), \c\ is U+001C (control-\), and so on. Our preprocessor treated \c as a plain one-char escape, which caused two problems:

• Bracket-end finder: scanning for the closing ] of a character class, \c] was misread as the class terminator.
• Class-content emitter: \cX was emitted to Java as-is, so Java's Pattern re-parsed sequences like \c\[ as control-backslash followed by an opening bracket — yielding a misleading Unclosed character class error.

Fix

• RegexPreprocessor.handleCharacterClass: skip the character following a \c escape when locating the closing ].
• RegexPreprocessorHelper.handleRegexCharacterClassEscape: detect \cX and convert it to \x{HH} using Perl semantics (uc(X) XOR 0x40, low byte). Java then sees a plain hex escape with no special semantics to misinterpret.

Motivation

XML/Dumper.pm:685 strips control chars with:

s/[\0\ca\cb\cc...\cz\c[\c\\c]\c^\c_]//g;

This regex previously failed with Regex compilation failed: Unclosed character class near index 89, taking down 8 of the 32 test files in jcpan -t Data::Serializer mid-run with non-zero exit status (the parent test scripts each die on regex compilation failure, so subtests after the failure were never reported).

Impact on jcpan -t Data::Serializer

	Before	After
Failed test programs	10/32	9/32
Subtests run	1250	1842
Subtests reported failed	13	13
Test files aborted	8	0

The remaining 9 failing programs are unrelated logic issues (Config::General uses (?(...)...) conditional patterns we don't implement; several files share a PHP::Serialization issue).

Test plan

• make (all unit tests pass)
• Added manual coverage: \ca..\cZ, \c[, \c\, \c], \c^, \c_, \c? all match the documented Perl values.
• jcpan -t Data::Serializer — XML::Dumper now passes; cascading regex crashes eliminated.
• jcpan -t Math::Base::Convert — still 5350/5350 passing (no regression).

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