🐛 Close broker and storage backend when verdi commands exit - #7552

`IdentifierParamType.convert` loaded an ORM entity, so merely parsing a
`verdi` command line opened the storage backend. That made the backend's
lifetime ambiguous: acquisition was a side effect of click's parameter
processing rather than something any command asked for.

Parameter types now validate the identifier and return it unchanged, and
expose `resolve()` for the lookup. Commands call the helpers in the new
`aiida.cmdline.utils.loaders` module, which locate the parameter that
supplied the identifier and delegate to its `resolve()`. The declaration
therefore stays the single source of truth: restrictions such as
`sub_classes` are declared once on the parameter instead of being
repeated in every command body.

Entity-dependent checks move from `convert` to `resolve` overrides, so
they still live on the type that owns them:

  * `CodeParamType` validates the calculation plugin.
  * `GroupParamType` creates the group when it does not exist.
  * `UserParamType` looks the user up by email and raises `NotExistent`
    or `MultipleObjectsError` rather than calling `fail`.

Failures are re-raised as `click.BadParameter` attributed to the
originating parameter, so the message and the exit code are unchanged
from parse-time conversion.

A few parameters are consumed while the command line is still being
parsed, because a later parameter derives its interactive default or its
validation from the loaded entity. Those use `resolve_callback`, which
loads the backend itself: `verdi computer duplicate`, `verdi code
create`/`duplicate`, `verdi user configure` and the `verdi computer
configure` subcommands.

Commands that relied on parameter conversion to load the backend as a
side effect now declare `with_dbenv` explicitly: the whole of
`verdi data core.remote`, `verdi data core.array/core.dict show`,
`verdi calcjob gotocomputer` and `verdi computer goto/configure show`.

BREAKING: `arguments.NODE`, `NODES`, `CODE`, `GROUP`, `COMPUTER`,
`PROCESS`, `USER` and friends now hand the command callback a `str`
identifier rather than an ORM entity. Plugins that reuse these
parameters must resolve the identifier themselves.

Two command bodies were left behind by the migration of ORM identifier
resolution out of the click param types and still treated their parameter
as an ORM entity:

* `verdi data core.bands list` reads `group.pk` off the `--groups` values,
  which come from the shared `list_options` decorator and so were invisible
  to the per-command sweep.
* `verdi devel launch-add` and `launch-multiply-add` pass `--code` straight
  to `get_builder()` and to the workchain inputs. Both declare the code
  through `options.CODE`, not `arguments.CODE`.

The `verdi devel` bodies already import `load_code` from `aiida.orm` for the
`bash@localhost` fallback, so the cmdline loaders are imported as a module to
keep the two lookups distinguishable.