Fix DevicePlugins.getPlugin for multi-site multi-period requests

[sgiehl]

Description

DevicePlugins.getPlugin fails when both multiple sites and multiple periods are requested together, for example:

idSite=1,2&period=day&date=last2

The method handled DataTable\Map results as if they were only one level deep. In the multi-site + multi-period case,
Matomo returns a nested map (site -> period -> DataTable), so the existing loop eventually processed an inner
DataTable\Map as if it were a leaf DataTable.

Fix

This change updates DevicePlugins.getPlugin to traverse the returned tables leaf-by-leaf using multiFilter(), keeping
these result sets aligned at every nesting level:

• plugin report table
• browser versions table
• nb_visits numeric table

The VisitsPercent processed metric is now added only to actual leaf DataTable instances, which makes the API work for:

• single site / single period
• single site / multi period
• multi site / single period
• multi site / multi period

Tests

Added an integration test covering a multi-site + multi-period request and verifying the nested result structure is
processed correctly.

Checklist

• [✔] I have understood, reviewed, and tested all AI outputs before use
• [✔] All AI instructions respect security, IP, and privacy rules

Review

• Functional review done
• Potential edge cases thought about (behaviour of the code with strange input, with strange internal state or possible interactions with other Matomo subsystems)
• Usability review done (is anything maybe unclear or think about anything that would cause people to reach out to support)
• Security review done
• Wording review done
• Code review done
• Tests were added if useful/possible
• Reviewed for breaking changes
• Developer changelog updated if needed
• New documentation added or existing documentation updated