Rewrite `Bounds` as a thin, deprecated subclass of
`frequenz.core.math.Interval[float | None]`, exposing the historical
`lower` / `upper` attribute names as deprecated `@property` aliases for
`Interval.start` / `Interval.end`.

`Bounds` now inherits Interval's validation, containment, string
conversion, and dataclass semantics; two overrides are added:

* `__eq__` — cross-compares against any `Interval` instance so
  `Bounds(lower=1, upper=2) == Interval(1, 2)` is `True`. Without this,
  dataclass-generated equality would reject mismatched types and break
  the migration UX.

* `__hash__` — restored (Python nullifies auto-hash whenever `__eq__`
  is overridden) and matches Interval's hashing of `(start, end)`.

Because `Bounds` now IS-A `Interval[float | None]`, code accepting
`Interval[float | None]` accepts `Bounds` instances. This unlocks
migrating field types on `MetricSample`, `ElectricalComponent`, and
`ElectricalComponentConnection` from `Bounds` to `Interval`
transparently.

Two visible behavioural changes on `Bounds`:

* Invalid-bounds `ValueError` message text moves from Bounds's old
  wording (`"Lower bound (X) must be less than or equal to upper bound
  (Y)"`) to Interval's (`"The start (X) can't be bigger than end (Y)"`).

* `str(Bounds(lower=None, upper=None))` now returns `"[∞, ∞]"` instead
  of `"[None, None]"` (`Interval`'s `__str__`).

We ignore the deprecation inside `bounds_from_proto()` to avoid a
double deprecation message because the function itself will be
deprecated in an upcoming commit.

Signed-off-by: Leandro Lucarella <luca-frequenz@llucax.com>

Change the `MetricSample.bounds` field type from `list[Bounds]` to
`Sequence[Interval[float | None]]`. `Sequence` (covariant) allows
callers to keep passing `list[Bounds]` now that `Bounds` is a subclass
of `Interval[float | None]`; it also accepts pure
`list[Interval[float | None]]`, `tuple[Interval[float | None], ...]`,
etc..

This is a soft-breaking type-level change: downstream code holding a
variable typed `list[Bounds]` and passing it to `MetricSample` still
type-checks under Sequence covariance, and code reading `sample.bounds`
still supports iteration and indexing but no longer supports `.append()`
or other list-mutation methods. Runtime behaviour is unchanged (the
class is frozen — mutation was never legal). Allowing mutation of a
frozen `dataclass` was a bug anyways, it should have never been allowed.

The internal proto converter `_metric_bounds_from_proto` is rewritten in
place to build `list[Interval[float | None]]` directly via
`bounds_from_proto2`, so freshly-parsed samples no longer carry
deprecated `Bounds` instances. Existing `bounds_from_proto` remains
unchanged (deprecation lands in a follow-up commit).

Signed-off-by: Leandro Lucarella <luca-frequenz@llucax.com>

Change the `metric_config_bounds` field on `ElectricalComponent` from
`Mapping[Metric | int, Bounds]` to `Mapping[Metric | int,
Interval[float | None]]`. `ElectricalComponent` is still unreleased, so
this is a direct type replacement, no need for backwards-compatibility.

The private converter `_metric_config_bounds_from_proto`, now calls
`bounds_from_proto2` internally so freshly-parsed components no longer
carry deprecated `Bounds` instances.

Signed-off-by: Leandro Lucarella <luca-frequenz@llucax.com>

Change the `operational_lifetime` field on `ElectricalComponent` and
`ElectricalComponentConnection` from `Lifetime` to
`Interval[datetime | None]`. Both classes are still unreleased, so this
is a direct type replacement, no backwards-compatibility needed.

The default factory yields an unbounded
`Interval[datetime | None](None, None)` matching the historical "always
operational" semantics of `Lifetime()`.

`lifetime_from_proto` is rewritten to return `Interval[datetime | None]`
directly.

The invalid-lifetime error message text in the affected tests moves
from `"Start (X) must be before or equal to end (Y)"` (from
`Lifetime.__post_init__`) to `"The start (X) can't be bigger than end
(Y)"` (from `Interval.__post_init__`).

The `Lifetime` class itself will be removed in a follow-up commit.

Signed-off-by: Leandro Lucarella <luca-frequenz@llucax.com>

Delete the `Lifetime` dataclass and its tests. `Lifetime` was added in
the current unreleased development cycle, and the previous commit
migrated every consumer to `frequenz.core.math.Interval`, so there is
no remaining user of the class.

The `lifetime_from_proto` conversion function stays — it still parses
`lifetime_pb2.Lifetime` protobuf messages, only its return type is now
`Interval[datetime | None]`.

Signed-off-by: Leandro Lucarella <luca-frequenz@llucax.com>

Mark the two `Bounds`-returning proto converters `bounds_from_proto*`
and `bounds_from_proto_with_issues` as `@deprecated`, pointing callers
at `bounds_from_proto2` and `bounds_from_proto_with_issues2`
respectively. Both new variants return
`frequenz.core.math.Interval[float | None]` and are already used by
every internal call site.

`bounds_from_proto_with_issues` delegates to `bounds_from_proto`; the
internal call is wrapped in `warnings.catch_warnings()` so callers of
`_with_issues` see one `DeprecationWarning` (the outer one), not two.

The internal `Bounds(...)` construction inside `bounds_from_proto`
remains wrapped in `warnings.catch_warnings()` (added when `Bounds`
became `@deprecated`), so the two suppressions compose correctly and
each caller entry point emits exactly one warning identifying its own
replacement symbol.

Signed-off-by: Leandro Lucarella <luca-frequenz@llucax.com>

Signed-off-by: Leandro Lucarella <luca-frequenz@llucax.com>