ephemeral run: Fix missing libgcc.so errors in entrypoint

[petracvv]

In some host distributions not all system libraries are in the top-level /usr/lib and /usr/lib64 directories. Since we are mounting /usr from the host into the container, we need to account for that by also mounting the local ld.so.cache

Fixes #296

I don't think we need to worry about libraries in /opt as the bcvk binary has very minimal linking requirements:

❯ ldd ~/.local/bin/bcvk
        linux-vdso.so.1 (0x00007f499d3de000)
        libgcc_s.so.1 => /usr/lib/gcc/x86_64-pc-linux-gnu/15/libgcc_s.so.1 (0x00007f499d382000)
        libm.so.6 => /usr/lib64/libm.so.6 (0x00007f499d26d000)
        libc.so.6 => /usr/lib64/libc.so.6 (0x00007f499ca14000)
        /lib64/ld-linux-x86-64.so.2 (0x00007f499d3e0000)

[gursewak1997]

Thanks for working on this.