Refactor library RPC implementation of `admire::update_adhoc_storage`

Similarly to #36 (closed), the actual implementation of the RPC should be moved to admire::detail in impl.[ch]pp similarly to admire::register|update|remove_job().

This should include:

• Input arg job type should be changed to admire::job.
• Input arg ctx type should be changed to admire::adhoc_storage::context.
• Input arg adhoc_storage should be changed to admire::adhoc_storage.
• Since errors can occur but there's no output arg, the return type of the new function should simply be an admire::error_code>.
• Updating the C++ examples to fit the new API.

This task also probably requires:

• Redefining the RPC types for the RPC defined in rpc_types.[ch]pp
• Using conversion types to manage RPC types without memory leaks.