Pretty-print save game XML by default

[ayrtondenner]

Context

From Discord #coding (2026-02-25), JonnyH noted that save game XML is written as one massive line, making it difficult to inspect without local pretty-print tools. The compressed size difference would be negligible.

man I really should get the code to pretty-print the save xml by default - one massive line is a PITA if you don't have local pretty-print tools to hand
and all to save a few bytes that probably compress well anyway... meh

TheSnide also suggested that auto-splitting into multiple files can sometimes help.

Proposal

Investigate enabling pretty-printed (indented) XML output for save games by default. The minor increase in uncompressed size should compress well and the readability benefit for debugging and modding is significant.

Tasks

• Identify where save game XML serialization happens
• Determine how to enable indented/pretty-printed output (pugixml supports this)
• Evaluate impact on save file size (compressed vs uncompressed)
• Consider whether splitting into multiple files is also worth exploring