feat: add postcodes:import command for loading ONSPD CSV

tests/Feature/Console/ImportPostcodesTest.php

@@ -0,0 +1,31 @@
+<?php
+
+use App\Models\Postcode;
+use Illuminate\Foundation\Testing\RefreshDatabase;
+
+uses(RefreshDatabase::class);
+
+function writeOnspdFixture(string $contents): string
+{
+    $path = tempnam(sys_get_temp_dir(), 'onspd_').'.csv';
+    file_put_contents($path, $contents);
+
+    return $path;
+}
+
+it('imports active postcodes from an ONSPD CSV', function (): void {
+    $csv = <<<'CSV'
+pcd,pcds,doterm,lat,long
+"SW1A1AA","SW1A 1AA","",51.501009,-0.141588
+"M11AD","M1 1AD",,53.480957,-2.237428
+CSV;
+
+    $path = writeOnspdFixture($csv);
+
+    $this->artisan('postcodes:import', ['--file' => $path])
+        ->assertSuccessful();
+
+    expect(Postcode::count())->toBe(2)
+        ->and(Postcode::find('SW1A1AA')->outcode)->toBe('SW1A')
+        ->and(Postcode::find('M11AD')->outcode)->toBe('M1');
+});