Narrow regex subject to decimal-int-string when every alternation branch is a decimal integer

[phpstan-bot]

Summary

preg_match() can narrow its subject parameter to decimal-int-string when the
pattern only matches decimal integers. For the common integer pattern
/^(?:0|-?[1-9][0-9]*)$/ PHPStan only narrowed the subject to non-empty-string.
This change makes alternations whose every branch is a decimal integer narrow the
subject (and the whole-match group) to decimal-int-string.

Changes

• src/Type/Regex/RegexGroupParser.php:
  • Replaced the decimalInteger($walkResult->isDecimalInteger()->and($decimalInteger))
    combination in the alternation branch of walkGroupAst() with a call to the new
    concatDecimalInteger() helper.
  • Added concatDecimalInteger(TrinaryLogic $left, TrinaryLogic $right): a
    non-decimal part forces no, a decimal part forces yes, otherwise maybe.
• tests/PHPStan/Analyser/nsrt/bug-14784.php: regression test plus analogous cases.

Root cause

Decimal-integer-ness of a string is the conjunction of its parts, but the running
state starts as maybe (nothing seen yet). The per-token logic upgrades maybe
to yes when it sees a digit. The alternation branch instead combined its
all-branches-decimal result into the running state with TrinaryLogic::and(), and
maybe->and(yes) is maybe — so an all-decimal alternation never committed to
yes. The whole match (subject base type) is computed from this walkGroupAst()
result, so the narrowing was lost for any pattern whose top-level shape is an
alternation. The new helper mirrors the token logic: a decimal part forces yes
regardless of the still-undetermined maybe prefix, while a non-decimal part still
forces no. The capturing-group element type is produced by a separate
root-alternation path (getRootAlternation()) and was already precise
('0'|(decimal-int-string&non-falsy-string)), so it was left untouched.

Test

tests/PHPStan/Analyser/nsrt/bug-14784.php reproduces the reported pattern and
covers analogous cases:

• the reported /^(?:0|-?[1-9][0-9]*)$/ (non-capturing) and its capturing variant,
• alternation of two decimal literals /^(?:0|123)$/,
• alternation without a leading sign /^(?:0|[1-9][0-9]*)$/,
• an alternation followed by required digits /^[0-9]+(?:0|5)$/,
• a negative case where a non-decimal branch (/^(?:0|abc)$/) keeps non-empty-string,
• the capturing-group element type.

Additionally verified via ad-hoc analysis that nested alternations
(/^(?:0|(?:1|2))$/), non-anchored patterns, empty-or-decimal alternations, and
hex alternations all infer the correct types. The full NodeScopeResolverTest
suite, the preg_match* shape tests, the regex type tests, and make phpstan
self-analysis all pass.

Fixes phpstan/phpstan#14784