fix: sticky bucket race condition causing JsonDecodingException crashes

[vazarkevych]

Problem

Users are facing the issue of a JsonDecodingException crash after updating to the 6.1.3 version when using the setAttributesSync function. The error shows concatenated JSON being read from the stickybucket cache.

Unexpected JSON token at offset 221: Expected EOF after parsing, but had { instead
JSON input: .....v3_iteration__4": "1" }{ "attributeName": "userId".....

Root cause

setAttributesSync and refreshStickyBucketService (triggered internally by feature fetching) both call refreshStickyBucketsSync concurrently without synchronization. The file-based CachingAndroid performs non-atomic -> delete -> create -> append, so concurrent read/write operations can produce corrupted JSON

Fix

• Add Mutex to GBUtils file to synchronize all sticky bucket read/write operations refreshStickyBucketsSync and saveStickyBucketAssignment. This prevents concurrent access to cache files.

• Remove manual Accept-Encoding header in GBNetworkDispatcherOkHttp and GBNetworkDispatcherKtor. They handle gzip decompression transparently by default.