Add T_PERCENT type to handle %4%-style format specifiers

[Copilot]

PHP's printf allows format specifiers ending in % with modifiers (e.g. %4%, %l%, %+5.5%). These differ from %%: they consume one argument (without using it), whereas %% consumes none. Previously these were emitted as invalid lexemes.

Changes

• ArgumentLexeme: adds T_PERCENT = '%' constant and includes it in VALID_T_TYPES. argType() returns ARG_TYPE_MISSING by default since T_PERCENT is not in any of the typed groups (INTEGER_TYPES, DOUBLE_TYPES, STRING_TYPES).
• %% special case: untouched — still emits a T_LITERAL_STRING and consumes no argument.

// Previously invalid — now parses as a valid T_PERCENT ArgumentLexeme
// consuming one argument slot with ARG_TYPE_MISSING
sprintf("%4%", $ignored);   // → "%"
sprintf("%l%", $ignored);   // → "%"
sprintf("%+5.5%", $ignored); // → "%"

// Still handled as the literal special case (no argument consumed)
sprintf("%%");              // → "%"

[Copilot]

Pull request overview

Adds support for PHP printf-compatible format specifiers that end in % but include modifiers (e.g. %4%, %l%, %+5.5%), treating them as valid argument-consuming lexemes instead of invalid ones.

Changes:

• Introduces ArgumentLexeme::T_PERCENT ('%') and includes it in VALID_T_TYPES so the parser recognizes %...% type specifiers.
• Extends integration coverage to verify parsing/serialization and that these specifiers consume exactly one argument (typed as ARG_TYPE_MISSING).

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
src/ArgumentLexeme.php	Adds the new T_PERCENT type and makes it a recognized valid type for parsing.
test/Integration/ParserTest.php	Adds parsing + argument-consumption test cases for %...% percent-type specifiers.

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