POSIX.pm already exported `setlocale`, `localeconv`, and the LC_* category
constants, but none of them had an implementation: any caller got
`Undefined subroutine &POSIX::setlocale`.

PerlOnJava cannot really switch the JVM/C locale, but adding minimal stubs
is enough for modules that just call `setlocale(LC_COLLATE, "C")` for its
return value or probe `localeconv()` for basic numeric formatting. The
stubs return the requested locale name (`C` by default) and a reasonable
default locale table.

Unblocks List::MoreUtils PP-mode minmaxstr.t (RC3 in
dev/modules/list_moreutils.md).

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Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

Perl treats the `my` declaration in
`my @long_list = EXPR for LIST;` / `my $x = EXPR while COND;` as
declared in the enclosing scope — the variable name is visible for the
rest of the block — while each loop iteration still creates a fresh
instance. Without this, the enclosing scope sees an undeclared variable
and `use strict` bails at compile time, e.g.:

    my @long_list = int rand(1000) for 0 .. 1E7;
    my @part      = part { ... } @long_list;   # strict error pre-fix

The parser now detects this pattern in the `for`/`foreach` and
`while`/`until` statement-modifier branches, emits a bare `my DECL;` in
the enclosing scope, and leaves the inner `my DECL = RHS` in the loop
body (wrapped in a BlockNode for `while`/`until` so the inner `my`
properly shadows the outer one). The end-of-loop value of the outer
variable matches perl: empty/undef, because the body's `my` introduces
a fresh per-iteration instance.

Unblocks List::MoreUtils PP-mode part.t (RC2 in
dev/modules/list_moreutils.md).

Generated with [Devin](https://devin.ai)

Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

Perl's split re-runs its regex at the end of each zero-width match with
REG_NOTEMPTY_ATSTART. When a consuming alternative of the pattern also
matches at that position, the consumed characters become an additional
separator and an empty field appears between the two separators, e.g.

    split /(?:\b|\s)/, "Lorem ipsum,"
    # ("Lorem", "", "ipsum", ",")

Java's Matcher tries alternations left-to-right and stops at the first
match, so `\b` always wins and the `\s` alternative is never attempted
at the same offset. Without compensation, the space leaks into the next
field and the empty separator disappears: jperl was returning
`("Lorem", " ", "ipsum", ",")`.

After each zero-width match, we now probe with `Matcher.matches()` on
regions of increasing length starting at matchEnd. The shortest region
the full pattern matches gives the length of the consuming alternative;
if found, we emit an empty field and advance past the consumed
characters.

Unblocks List::MoreUtils PP-mode mode.t (RC4 in
dev/modules/list_moreutils.md).

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Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

Perl emits
    Use of uninitialized value in array element
    Use of uninitialized value in hash element
whenever an undef is used as a subscript under `use warnings`. PerlOnJava
wasn't producing this diagnostic, which made it impossible to test
patterns like `$parts[$code->($_)]` where `$code` returns undef.

The warning is emitted from the RuntimeArray.get / RuntimeHash.get
entry points, covering both the rvalue read path and the lvalue / autoviv
path (both go through get()).

Unblocks List::MoreUtils PP-mode part.t warnings checks (RC5 in
dev/modules/list_moreutils.md).

Generated with [Devin](https://devin.ai)

Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

…en branch