Resolve "Use mochi-thallium instead of our custom Margo engine"

This MR removes our in-house C++ engine for Margo and replaces it with 
mochi-thallium. This makes code simpler since the daemon implementation can 
be fully in C++, which prevents having to muck with C types and their 
lifetimes.

Closes #109

See merge request !74

Resolve "Use C++20"

Closes #108

See merge request !73

Merge branch 'amiranda/102-refactor-library-rpc-implementation-of-admire-remove_pfs_storage' into 'main'

Resolve "Refactor library RPC implementation of `admire::remove_pfs_storage`"

Closes #102

See merge request !71

Merge branch 'amiranda/101-refactor-library-rpc-implementation-of-admire-update_pfs_storage' into 'main'

Resolve "Refactor library RPC implementation of `admire::update_pfs_storage`"

Closes #101

See merge request !70

Merge branch 'amiranda/104-build-breaks-due-to-missing-tl-expected-commit-job-failed-30188' into 'main'

Resolve "Build breaks due to missing `tl::expected` commit (Job Failed #30188)"

Closes #104

See merge request !72

Fixes #104

Resolve "Refactor RPC implementation of `admire::register_pfs_storage`"

This MR moves the implementation of the RPC construction for
`ADM_register_pfs_storage` to `admire::detail` in `impl.[ch]pp`
similarly to other RPCs already refactored. This includes changing
the C ADM_types to native C++ types.

Closes #99

See merge request !68

Merge branch 'amiranda/100-c-api-should-have-adm_adhoc_storage_t-and-adm_pfs_storage_t-types' into 'main'

Resolve "C API should have `ADM_adhoc_storage_t` and `ADM_pfs_storage_t` types"

This MR eliminates the `ADM_storage_t` from the C API and its 
corresponding `admire::storage` type from the C++ API to simplify
the usage and the implementation. 

Instead, the types `ADM_adhoc_storage_t` and `ADM_pfs_storage_t` 
are created for the C API, which correspond to the already existing 
types `admire::adhoc_storage` and `admire::pfs_storage`, which no 
longer inherit from `admire::storage`.

Additionally, this MR also removes `ADM_storage_type_t`, replacing it
with `ADM_adhoc_storage_type_t` and `ADM_pfs_storage_type_t`, and 
renames their values with the appropriate `ADM_ADHOC_` and `ADM_PFS_`
prefixes.

Closes #100

See merge request !69