Centralize logs in the correct QGIS logging panel

[yan-sln]

Review and centralize plugin logging (avoid logs leaking into Processing tab)

Context

Some plugin logs currently appear inside the QGIS Processing panel instead of the dedicated plugin/message logging location.

This likely happens because parts of the code use:

• QgsProcessingFeedback
• processing feedback streams
• direct processing outputs

The result is inconsistent logging behavior:

• some messages appear in the plugin logs
• others appear in the Processing tab
• user feedback is fragmented

Problem

The plugin should provide a single, coherent logging experience.

Currently:

• operational logs are split across multiple panels
• Processing feedback messages pollute the Processing tab
• users may miss important information

Proposed improvement

Audit the logging system and ensure all plugin logs are routed consistently through:

• QgsMessageLog
• the dedicated logging category (e.g. Secateur)

while keeping Processing feedback only for actual processing progress when necessary.

Expected behavior :

• plugin logs appear in a single consistent location
• Processing tab is not flooded by internal plugin logs
• warning/error/debug levels are standardized
• feedback remains readable during long operations