Add single channel mode feature.

The addition of a single-channel mode implied further modularisation of the component. This commit has broken the component down into the following modules to avoid a huge single source file and to make unit testing easier.

The modules:

- Separation of public and private code
- *types and *defs
- public relay_chn API
- *adapter
- *output
- *run_info
- *core
- *ctl (control)
- *tilt

Closes #957.

private_include/relay_chn_ctl.h

@@ -0,0 +1,56 @@
+/*
+ * SPDX-FileCopyrightText: 2025 Kozmotronik Tech developer@kozmotronik.com.tr
+ *
+ * SPDX-License-Identifier: MIT
+ *
+ * Expose the *_ctl functions required by *_core.c file.
+ */
+
+#pragma once
+
+#include "relay_chn_priv_types.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/**
+ * @brief Initialize the relay channel control.
+ * 
+ * @param output Pointer to the output object(s).
+ * @param run_info Pointer to the runtime information object(s).
+ * 
+ * @return esp_err_t Returns ESP_OK on success, or an error code on failure.
+ */
+esp_err_t relay_chn_ctl_init(relay_chn_output_t *output, relay_chn_run_info_t *run_info);
+
+/**
+ * @brief Deinitialize the relay channel control.
+ * 
+ * This function cleans up resources used by the relay channel control.
+ */
+void relay_chn_ctl_deinit(void);
+
+#if RELAY_CHN_COUNT > 1
+/**
+ * @brief Get the control structure for a specific relay channel.
+ * 
+ * @param chn_id The ID of the relay channel to retrieve.
+ * 
+ * @return relay_chn_ctl_t* Pointer to the control structure for the specified channel, or NULL if not found.
+ */
+relay_chn_ctl_t *relay_chn_ctl_get(uint8_t chn_id);
+
+/**
+ * @brief Get the control structures for all relay channels.
+ * 
+ * @return relay_chn_ctl_t* Pointer to the array of control structures for all channels.
+ */
+relay_chn_ctl_t *relay_chn_ctl_get_all(void);
+#else
+relay_chn_ctl_t *relay_chn_ctl_get(void);
+#endif // RELAY_CHN_COUNT > 1
+
+#ifdef __cplusplus
+}
+#endif