Refactor NimBLEAttValue.

* Add length parameter to `setValue()` templates, with defaults for backward compatibility.
* Changed `setValue(const char*)` to add an optional length parameter so that a NULL character can be included, defaults to strlen.
* Moved non-inline functions to `NimBLEAttValue.cpp` file.
* Corrected includes to permit compilation as a stand-alone utility.
* Removed repeated code in `setValue()` by using `append()` after clearing the value.
* General code cleanup.

# Conflicts:
#	CMakeLists.txt

src/NimBLEAttValue.cpp

@@ -0,0 +1,130 @@
+/*
+ * NimBLEAttValue.cpp
+ *
+ *  Created: on July 17, 2024
+ *      Author H2zero
+ *
+ */
+
+#include "nimconfig.h"
+#if defined(CONFIG_BT_ENABLED)
+
+# if defined(CONFIG_NIMBLE_CPP_IDF)
+#  include "nimble/nimble_npl.h"
+# else
+#  include "nimble/nimble/include/nimble/nimble_npl.h"
+# endif
+
+# include "NimBLEAttValue.h"
+
+// Default constructor implementation.
+NimBLEAttValue::NimBLEAttValue(uint16_t init_len, uint16_t max_len)
+    : m_attr_value{static_cast<uint8_t*>(calloc(init_len + 1, 1))},
+      m_attr_max_len{std::min<uint16_t>(BLE_ATT_ATTR_MAX_LEN, max_len)},
+      m_attr_len{},
+      m_capacity{init_len}
+# if CONFIG_NIMBLE_CPP_ATT_VALUE_TIMESTAMP_ENABLED
+      ,
+      m_timestamp{}
+# endif
+{
+    NIMBLE_CPP_DEBUG_ASSERT(m_attr_value);
+}
+
+// Value constructor implementation.
+NimBLEAttValue::NimBLEAttValue(const uint8_t *value, uint16_t len, uint16_t max_len)
+: NimBLEAttValue(len, max_len) {
+    memcpy(m_attr_value, value, len);
+    m_attr_value[len] = '\0';
+    m_attr_len        = len;
+}
+
+// Destructor implementation.
+NimBLEAttValue::~NimBLEAttValue() {
+    if (m_attr_value != nullptr) {
+        free(m_attr_value);
+    }
+}
+
+// Move assignment operator implementation.
+NimBLEAttValue& NimBLEAttValue::operator=(NimBLEAttValue&& source) {
+    if (this != &source) {
+        free(m_attr_value);
+        m_attr_value   = source.m_attr_value;
+        m_attr_max_len = source.m_attr_max_len;
+        m_attr_len     = source.m_attr_len;
+        m_capacity     = source.m_capacity;
+        setTimeStamp(source.getTimeStamp());
+        source.m_attr_value = nullptr;
+    }
+
+    return *this;
+}
+
+// Copy assignment implementation.
+NimBLEAttValue& NimBLEAttValue::operator=(const NimBLEAttValue& source) {
+    if (this != &source) {
+        deepCopy(source);
+    }
+    return *this;
+}
+
+// Copy all the data from the source object to this object, including allocated space.
+void NimBLEAttValue::deepCopy(const NimBLEAttValue& source) {
+    uint8_t* res = static_cast<uint8_t*>(realloc(m_attr_value, source.m_capacity + 1));
+    NIMBLE_CPP_DEBUG_ASSERT(res);
+
+    ble_npl_hw_enter_critical();
+    m_attr_value   = res;
+    m_attr_max_len = source.m_attr_max_len;
+    m_attr_len     = source.m_attr_len;
+    m_capacity     = source.m_capacity;
+    setTimeStamp(source.getTimeStamp());
+    memcpy(m_attr_value, source.m_attr_value, m_attr_len + 1);
+    ble_npl_hw_exit_critical(0);
+}
+
+// Set the value of the attribute.
+bool NimBLEAttValue::setValue(const uint8_t* value, uint16_t len) {
+    m_attr_len = 0; // Just set the value length to 0 and append instead of repeating code.
+    append(value, len);
+    return memcmp(m_attr_value, value, len) == 0 && m_attr_len == len;
+}
+
+// Append the new data, allocate as necessary.
+NimBLEAttValue& NimBLEAttValue::append(const uint8_t* value, uint16_t len) {
+    if (len == 0) {
+        return *this;
+    }
+
+    if ((m_attr_len + len) > m_attr_max_len) {
+        NIMBLE_LOGE("NimBLEAttValue", "val > max, len=%u, max=%u", len, m_attr_max_len);
+        return *this;
+    }
+
+    uint8_t* res     = m_attr_value;
+    uint16_t new_len = m_attr_len + len;
+    if (new_len > m_capacity) {
+        res        = static_cast<uint8_t*>(realloc(m_attr_value, (new_len + 1)));
+        m_capacity = new_len;
+    }
+    NIMBLE_CPP_DEBUG_ASSERT(res);
+
+# if CONFIG_NIMBLE_CPP_ATT_VALUE_TIMESTAMP_ENABLED
+    time_t t = time(nullptr);
+# else
+    time_t t = 0;
+# endif
+
+    ble_npl_hw_enter_critical();
+    memcpy(res + m_attr_len, value, len);
+    m_attr_value             = res;
+    m_attr_len               = new_len;
+    m_attr_value[m_attr_len] = '\0';
+    setTimeStamp(t);
+    ble_npl_hw_exit_critical(0);
+
+    return *this;
+}
+
+#endif // CONFIG_BT_ENABLED