feat(rows): add Rows::wasApplied() for lightweight transactions

[CodeLieutenant]

What

Adds Cassandra\Rows::wasApplied(): bool.

A conditional write returns an [applied] column instead of an empty result. Until now the only way to read it was:

if ($rows->first()['[applied]'] === false) { /* ... */ }

Now:

if (! $rows->wasApplied()) {
    $current = $rows->first();   // the conflicting values
}

Semantics

wasApplied() reads the [applied] column of the first row. A statement with no condition has no such column, and the method then returns true, so a caller can ask this of any result. This matches wasApplied() in the Java driver and was_applied in the Python driver.

false means the condition failed, not that the row is present:

Statement	wasApplied() === false means
IF NOT EXISTS	The row is already there
IF EXISTS	The row is not there
IF col = ?	The current value does not match

This is why the method is not named exists() — the meaning inverts with the condition, which the driver cannot see.

Implementation

The method reads the already-decoded row array, so it adds no cass_* call and no round trip. The [applied] column stays readable through first() and array access, so old code keeps working.

Also in this PR

Two stale statements in CLAUDE.md:

• It said to commit *_arginfo.h. That file is gitignored (.gitignore: src/**/*_arginfo.h) and generated at build time by cmake/GenStubs.cmake.
• It said to run gen_stub.php directly. Upstream gen_stub.php fails on declare(strict_types=1); with Unexpected node Stmt_Declare. The build calls tools/gen_stub/gen_arginfo.sh, which strips the declare first.

Tests

New tests/Feature/Results/LightweightTransactionTest.php, 7 cases:

• IF NOT EXISTS that wins, and one that loses (checks the current values come back)
• IF EXISTS against a missing row
• A failed IF col = ?
• A write with no condition
• A SELECT
• A result fetched through executeAsync()

All 13 tests in tests/Feature/Results pass against ScyllaDB, built with the DebugPHP8.4NTS preset.

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