fix(build): create output parent directory before native link

[alwaysLinger]

Observed failure

When the configured output path lives inside a directory that does not exist yet, the build compiles every source (minutes on a real project) and only then dies with a bare linker error:

# project.yml
name: app
sources:
  - app.php
output: artifacts/app

$ php bin/tpc.php project.yml -O2
...
Successfully compiled 6 files
/usr/bin/ld: cannot open output file /tmp/etest/artifacts/app: No such file or directory
collect2: error: ld returned 1 exit status
Fatal error: link failed: /tmp/etest/artifacts/app

The compiler could not have produced the artifact regardless of how long it compiled: the linker never creates parent directories, and nothing before the link creates them either.

Root cause

NativeBuilder::link() (src/Build/NativeBuilder.php) execs the link command without ensuring the target's parent directory exists. The Nano path is asymmetric evidence that this is an omission rather than a design choice: NativeSourceProjectBuilder already calls ensureDirectory(dirname($project->output)) right before linking (src/Build/NativeSourceProjectBuilder.php), but the plain tpc.php file.php -o ... / project.yml path has no equivalent.

Fix

NativeBuilder::link() now ensures the output parent directory exists (recursively) before invoking the linker, following the same ensureDirectory() pattern already used on the Nano path and in AtomicFile, EmbeddedArchiveBuilder and EmbeddedOpcodeGenerator:

private function ensureDirectory(string $directory): void
{
    if (!is_dir($directory) && !mkdir($directory, 0777, true) && !is_dir($directory)) {
        throw new \RuntimeException("Cannot create output directory: {$directory}");
    }
}

Translator::linkNativeTarget() converts the exception into the regular CLI fatal error, so a misconfigured output path now fails with Cannot create output directory: ... instead of a raw ld message.

Both entry points go through the same link call, so output: in project.yml and the -o CLI flag are covered, as is the embed SAPI target (which links through linkNativeTarget() as well).