APIServer: Add support for filtering to list rpc (#1175)

This is not intended to be used to support `--filter` or similar on the
CLIs list yet, it's solely to clean up our rather awkward use of
`ContainerClient.list()` today in the CLI. The list RPC simply returns
all of the containers we have created. Because of this, for a LOT of our
commands we filter to what we need client side, which feels like a
waste.. This change introduces a filter struct that we can provide an
array of container IDs, labels, and the status of the containers to
filter the `list()` output from.

This additionally, because it was killing (pun not intended) me and I
was already having to change this area for the `list()` additions,
changes container kill slightly to return an error if you try and kill a
container that doesn't exist.

Sources/ContainerResource/Container/ContainerListFilters.swift

@@ -0,0 +1,40 @@
+//===----------------------------------------------------------------------===//
+// Copyright © 2026 Apple Inc. and the container project authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//   https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//===----------------------------------------------------------------------===//
+
+import Foundation
+
+/// Filters for listing containers.
+public struct ContainerListFilters: Sendable, Codable {
+    /// Filter by container IDs. If non-empty, only containers with matching IDs are returned.
+    public var ids: [String]
+    /// Filter by container status.
+    public var status: RuntimeStatus?
+    /// Filter by labels. All specified labels must match.
+    public var labels: [String: String]
+
+    /// No filters applied. Will return all containers.
+    public static let all = ContainerListFilters()
+
+    public init(
+        ids: [String] = [],
+        status: RuntimeStatus? = nil,
+        labels: [String: String] = [:]
+    ) {
+        self.ids = ids
+        self.status = status
+        self.labels = labels
+    }
+}