* fix(proxy): allow model instances in LiteLLM_EndUserTable validation
* fix(proxy): preserve property-backed attributes when coercing spend
* refactor(proxy): default null end-user spend with a field validator
* fix(proxy): drop model-wide from_attributes from the end-user table
* test(proxy): unskip the /customer/block integration contracts
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Co-authored-by: mateo-berri <277851410+mateo-berri@users.noreply.github.com>