fix(nvs): fix hard-coded ns/key in bool overloads (#242)

* fix(nvs): fix hard-coded ns/key in bool overloads
* Add additional functions to take string_views
* Add error codes and update logging
* Update example to test more cases
* Update readme

* add screenshots to readme

components/nvs/example/README.md

@@ -21,3 +21,9 @@ idf.py -p PORT flash monitor
 (To exit the serial monitor, type ``Ctrl-]``.)
 
 See the Getting Started Guide for full steps to configure and use ESP-IDF to build projects.
+
+## Example Output
+
+![CleanShot 2024-05-18 at 12 54 46](https://github.com/esp-cpp/espp/assets/213467/60b2db2f-8796-4ae3-9a8c-51f69fa21911)
+![CleanShot 2024-05-18 at 12 54 54](https://github.com/esp-cpp/espp/assets/213467/ddceddbf-0690-4590-93b6-66cf91ad1898)
+![CleanShot 2024-05-18 at 12 55 02](https://github.com/esp-cpp/espp/assets/213467/1181fc79-f7bd-4b1d-b351-e5ca24ee7c55)

components/nvs/example/main/nvs_example.cpp

@@ -23,6 +23,35 @@ extern "C" void app_main(void) {
   ec.clear();
   fmt::print("Reset Counter = {}\n", counter);
 
+  bool flag = false;
+  nvs.get_or_set_var("other-namespace", "flag", flag, flag, ec);
+  ec.clear();
+  fmt::print("Got / Set Flag = {}\n", flag);
+  // now toggle the flag
+  flag = !flag;
+  nvs.set_var("other-namespace", "flag", flag, ec);
+  ec.clear();
+  fmt::print("Toggled Flag = {}\n", flag);
+
+  // test protection against really long namespace names (length > 15)
+  std::string long_ns(16, 'a');
+  nvs.get_or_set_var(long_ns, "flag", flag, flag, ec);
+  if (ec) {
+    fmt::print("Expected error: {}\n", ec.message());
+  } else {
+    fmt::print("Unexpected success\n");
+  }
+  ec.clear();
+
+  // test getting a non-existent key
+  nvs.get_var("system", "not-here", counter, ec);
+  if (ec) {
+    fmt::print("Expected error: {}\n", ec.message());
+  } else {
+    fmt::print("Unexpected success\n");
+  }
+  ec.clear();
+
   counter++;
 
   if (counter > 10) {