deps: isolate LMDB source builds
Extract LMDB into each build directory because its build writes objects into the source tree. Sharing that tree let an instrumented PGO stage contaminate later stages with incompatible objects.
Co-authored-by: Claude Fable 5 <noreply@anthropic.com>
Co-authored-by: OpenAI Codex <codex@openai.com>
