Refactor freqman_db parsing (#1244)

* WIP freqman changes/memory perf/stash
* Split ui tone_key function out for testing.
* Add more tests and fix bugs.
* Use default max_entries in recond
* Set limit back to 90 for now

firmware/application/file_reader.hpp

@@ -36,7 +36,8 @@
  */
 
 /* Iterates lines in buffer split on '\n'.
- * NB: very basic iterator impl, don't try anything fancy with it. */
+ * NB: very basic iterator impl, don't try anything fancy with it.
+ * For example, you _must_ deref the iterator after advancing it. */
 template <typename BufferType>
 class BufferLineReader {
    public:
@@ -133,4 +134,18 @@ using FileLineReader = BufferLineReader<File>;
  * are used or they will dangle. */
 std::vector<std::string_view> split_string(std::string_view str, char c);
 
+/* Returns the number of lines in a file. */
+template <typename BufferType>
+uint32_t count_lines(BufferLineReader<BufferType>& reader) {
+    uint32_t count = 0;
+    auto it = reader.begin();
+
+    do {
+        *it;  // Necessary to force the file read.
+        ++count;
+    } while (++it != reader.end());
+
+    return count;
+}
+
 #endif