Raise PHPStan to level 5 and clear what it found [ignore_release]

[snake14]

Description

Raises the plugin's base PHPStan level from 1 to 5, per PG-4897's ratchet step, and clears what that surfaced.

The level raise and the duplicated is_null($this->minBandwidth) check in VisitorDetails::handleProfileAction() are carried across from #104, which targeted 5.x-dev and predates the shared Plugins CI umbrella. That check can never fire: the min() on the line above returns one of two arguments that are both already non-null.

Level 5 then reported property_exists($view->config, 'selectable_columns') in configureViewDataTable() as always true — core declares that property on ViewDataTable\Config and every visualisation config extends it. Its sibling guard on Numeric::$byteSizeUnit goes with it: PHPStan does not flag that one, but the property has been in core since 2022 and is present at the 6.0.0-b1 tag, so the comment saying it may be missing is not true of any Matomo this plugin supports.

No behaviour changes on any supported version — all three removals are unreachable branches.

Issue No

Related to PG-4897. Replaces #104.

Steps to Replicate the Issue

Not applicable — this raises static analysis coverage rather than fixing a defect.

Checklist

• [✔] Tested locally or on demo2/demo3?
• [NA] New test case added/updated?
• [NA] Are all newly added texts included via translation?
• [NA] Are text sanitized properly? (Eg use of v-text v/s v-html for vue)
• [✖] Version bumped?
• [✔] I have understood, reviewed, and tested all AI outputs before use
• [✔] All AI instructions respect security, IP, and privacy rules
• [NA] Documentation updated?