common: force C locale for numeric formatting

[Scottcjn]

Summary

Ensure consistent decimal point formatting across all llama.cpp tools by forcing LC_NUMERIC to "C" locale.

Problem

On systems with non-English LC_NUMERIC locale (e.g. de_DE.UTF-8), different llama.cpp tools produce inconsistent decimal formatting:

Tool	Output	Reason
llama-cli	10000,0 (comma)	console::init() calls setlocale(LC_ALL, "")
llama-perplexity	10000.0 (period)	Default C locale unchanged

This affects all floating-point output including sampler parameters, performance stats, and model metadata — not just GGUF KV data.

Fix

Two-pronged approach:

1. common_init() in common.cpp: Set LC_NUMERIC to "C" early — catches all tools on startup
2. console::init() in console.cpp: Override LC_NUMERIC back to "C" after setlocale(LC_ALL, "") — prevents the user locale call from re-overriding the numeric locale

This keeps the user's locale for character handling (UTF-8, wide chars) while forcing consistent period-as-decimal-separator for all numeric output.

Testing

To verify on a system with German locale:

export LC_NUMERIC=de_DE.UTF-8
./llama-cli -m model.gguf -p "test" -n 1 2>&1 | grep -E '[0-9][,\.][0-9]'
# Before: 10000,0 (comma)
# After:  10000.0 (period)

Fixes #10613

🤖 Generated with Claude Code

[CISC]

Incorrect fix (making a library change global locale) and essentially duplicate of #17331