feat: Adds minimal cli executable and commands.

Sources/CLI/Commands/Convert.swift

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+import ArgumentParser
+import Dependencies
+import ManualDClient
+
+struct ConvertCommand: AsyncParsableCommand {
+
+  static let configuration = CommandConfiguration(
+    commandName: "convert",
+    abstract: "Convert to an equivalent recangular size."
+  )
+
+  @Option(
+    name: .shortAndLong,
+    help: "The height"
+  )
+  var height: Int
+
+  @Argument(
+    // name: .shortAndLong,
+    help: "The round size."
+  )
+  var roundSize: Int
+
+  func run() async throws {
+    @Dependency(\.manualD) var manualD
+
+    let size = try await manualD.rectangularSize(
+      round: .init(roundSize),
+      height: .init(height)
+    )
+
+    print("\(size.width) x \(height)")
+  }
+
+}

Sources/CLI/Commands/Size.swift

@@ -0,0 +1,35 @@
+import ArgumentParser
+import Dependencies
+import ManualDClient
+
+struct SizeCommand: AsyncParsableCommand {
+  static let configuration = CommandConfiguration(
+    commandName: "size",
+    abstract: "Calculate the required size of a duct."
+  )
+
+  @Option(
+    name: .shortAndLong,
+    help: "The design friction rate."
+  )
+  var frictionRate: Double = 0.06
+
+  @Argument(
+    help: "The required CFM for the duct."
+  )
+  var cfm: Int
+
+  func run() async throws {
+    @Dependency(\.manualD) var manualD
+
+    let size = try await manualD.ductSize(cfm: cfm, frictionRate: frictionRate)
+    print(
+      """
+      Calculated: \(size.calculatedSize.string(digits: 2))
+      Final Size: \(size.finalSize)
+      Flex Size: \(size.flexSize)
+      """
+    )
+
+  }
+}