Bug: Turkish Locale - Potential Header/Key resolution failure due to case-insensitive TreeMap serialization

Bug Description

Applications utilizing this SDK on a Turkish OS locale face unexpected anomalies or token crashes during HTTP header parsing.

Root Cause

In openai-java-core/src/main/kotlin/com/openai/core/http/Headers.kt (Line 38), the headers map is initialized using a locale-dependent comparison mechanism:

private val map: MutableMap<String, MutableList<String>> =
    TreeMap(String.CASE_INSENSITIVE_ORDER)

Java's native String.CASE_INSENSITIVE_ORDER internally triggers Character.toLowerCase(). On a Turkish host machine, this converts the capital letter I in "OpenAI-Organization" into a dotless ı, turning it into "openaı-organization".
This causes key lookup failures or broken token states when downstream interceptors (like OkHttp) process standard ASCII headers.

Related Upstream Issue

This is the Java/Kotlin ecosystem equivalent of the localization bug found in the Node SDK.

• Linked Node Issue: https://github.com/openai/openai-node/issues/1928

Suggested Official Fix

The TreeMap should enforce a locale-invariant comparator (such as Locale.ROOT) to guarantee strict ASCII/English-based casing rules across all operating systems:

TreeMap { s1, s2 -> s1.lowercase(java.util.Locale.ROOT).compareTo(s2.lowercase(java.util.Locale.ROOT)) }

Start in openai-java-core/src/main/kotlin/com/openai/core/http/Headers.kt at the TreeMap initialization. Reproduce header lookup or token parsing under a Turkish OS locale and verify the comparison is locale-invariant. Done means standard headers such as OpenAI-Organization resolve consistently regardless of the host locale.