Add LSTM to ngen extern

[arpita0911patel]

https://github.com/CIROH-UA/lstm

[JoshCu]

added in add_lstm_extern which was merged into #2 too.

adding to ngiab is just these two lines in the final image stage

COPY --from=ngen_clone /ngen/ngen/extern/lstm/lstm /ngen/ngen/extern/lstm
RUN uv pip install --no-cache-dir /ngen/ngen/extern/lstm --extra-index-url https://download.pytorch.org/whl/cpu

the extra index parameter installs cpu only pytorch which reduces the image size by ~5Gb

[JoshCu]

now also in the ngiab branch which will be used for nextgen in a box from now on