feat: Refactor MeshService into smaller, single-responsibility components (#4108)

Signed-off-by: James Rich <2199651+jamesarich@users.noreply.github.com>

app/src/test/java/com/geeksville/mesh/service/MeshCommandSenderTest.kt

@@ -0,0 +1,75 @@
+/*
+ * Copyright (c) 2025 Meshtastic LLC
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+package com.geeksville.mesh.service
+
+import org.junit.Assert.assertEquals
+import org.junit.Assert.assertNotEquals
+import org.junit.Before
+import org.junit.Test
+import org.meshtastic.core.database.entity.NodeEntity
+import org.meshtastic.core.model.DataPacket
+import org.meshtastic.proto.user
+
+class MeshCommandSenderTest {
+
+    private lateinit var commandSender: MeshCommandSender
+    private lateinit var nodeManager: MeshNodeManager
+
+    @Before
+    fun setUp() {
+        nodeManager = MeshNodeManager()
+        commandSender = MeshCommandSender(null, nodeManager, null, null)
+    }
+
+    @Test
+    fun `generatePacketId produces unique non-zero IDs`() {
+        val ids = mutableSetOf<Int>()
+        repeat(1000) {
+            val id = commandSender.generatePacketId()
+            assertNotEquals(0, id)
+            ids.add(id)
+        }
+        assertEquals(1000, ids.size)
+    }
+
+    @Test
+    fun `resolveNodeNum handles broadcast ID`() {
+        assertEquals(DataPacket.NODENUM_BROADCAST, commandSender.resolveNodeNum(DataPacket.ID_BROADCAST))
+    }
+
+    @Test
+    fun `resolveNodeNum handles hex ID with exclamation mark`() {
+        assertEquals(123, commandSender.resolveNodeNum("!0000007b"))
+    }
+
+    @Test
+    fun `resolveNodeNum handles custom node ID from database`() {
+        val nodeNum = 456
+        val userId = "custom_id"
+        val entity = NodeEntity(num = nodeNum, user = user { id = userId })
+        nodeManager.nodeDBbyNodeNum[nodeNum] = entity
+        nodeManager.nodeDBbyID[userId] = entity
+
+        assertEquals(nodeNum, commandSender.resolveNodeNum(userId))
+    }
+
+    @Test(expected = IllegalArgumentException::class)
+    fun `resolveNodeNum throws for unknown ID`() {
+        commandSender.resolveNodeNum("unknown")
+    }
+}