Fix OSM API gzip response handling

[gitmur444]

Problem Description

The map-machine currently fails with "Cannot download data" error when trying to download data from the OpenStreetMap API in some environments (particularly Docker containers). This happens because the OSM API returns gzip-compressed responses, but the code in osm_getter.py expects the response to start with an XML opening bracket <.

Root Cause

When the OSM API returns compressed (gzip) data, the binary content starts with gzip magic bytes \x1f\x8b instead of XML's <. This causes map-machine to reject the response as invalid and raise a "Cannot download data" error.

Evidence and Logs

With original code, when downloading a larger area:

INFO Getting https://api.openstreetmap.org/api/0.6/map...
CRITICAL Cannot download data.

With the fixed code, we get a proper error for large areas:

INFO Getting https://api.openstreetmap.org/api/0.6/map...
CRITICAL Cannot download data: too many nodes (limit is 50000). Try to request smaller area.

And for appropriately sized areas, it works correctly:

INFO Getting https://api.openstreetmap.org/api/0.6/map...
INFO Constructing ways...
INFO Constructing nodes...
INFO Drawing ways...
INFO Drawing main icons...
INFO Drawing extra icons...
INFO Drawing texts...
INFO Writing output SVG to output/paris_small_area_fixed.svg...

[enzet]

@gitmur444 Sorry that it took me so long to merge it. And thank you for one of the most well-documented PRs I've ever seen.