Add some docstrings

lib/search/filter_kanji.dart

@@ -1,6 +1,9 @@
 import 'package:jadb/table_names/kanjidic.dart';
 import 'package:sqflite_common/sqflite.dart';
 
+/// Filters a list of kanji characters, returning only those that exist in the database.
+///
+/// If [deduplicate] is true, the returned list will deduplicate the input kanji list before returning the filtered results.
 Future<List<String>> filterKanjiWithDbConnection(
   DatabaseExecutor connection,
   List<String> kanji,

lib/search/kanji_search.dart

@@ -3,9 +3,9 @@ import 'package:jadb/models/kanji_search/kanji_search_radical.dart';
 import 'package:jadb/models/kanji_search/kanji_search_result.dart';
 import 'package:jadb/table_names/kanjidic.dart';
 import 'package:jadb/table_names/radkfile.dart';
-import 'package:jadb/util/romaji_transliteration.dart';
 import 'package:sqflite_common/sqflite.dart';
 
+/// Searches for a kanji character and returns its details, or null if the kanji is not found in the database.
 Future<KanjiSearchResult?> searchKanjiWithDbConnection(
   DatabaseExecutor connection,
   String kanji,
@@ -214,6 +214,7 @@ Future<KanjiSearchResult?> searchKanjiWithDbConnection(
 
 // TODO: Use fewer queries with `IN` clauses to reduce the number of queries
 
+/// Searches for multiple kanji at once, returning a map of kanji to their search results.
 Future<Map<String, KanjiSearchResult>> searchManyKanjiWithDbConnection(
   DatabaseExecutor connection,
   Set<String> kanji,

lib/search/radical_search.dart

@@ -3,6 +3,10 @@ import 'package:sqflite_common/sqlite_api.dart';
 
 // TODO: validate that the list of radicals all are valid radicals
 
+/// Returns a list of radicals that are part of any kanji that contains all of the input radicals.
+///
+/// This can be used to limit the choices of additional radicals provided to a user,
+/// so that any choice they make will still yield at least one kanji.
 Future<List<String>> searchRemainingRadicalsWithDbConnection(
   DatabaseExecutor connection,
   List<String> radicals,
@@ -31,6 +35,7 @@ Future<List<String>> searchRemainingRadicalsWithDbConnection(
   return remainingRadicals;
 }
 
+/// Returns a list of kanji that contain all of the input radicals.
 Future<List<String>> searchKanjiByRadicalsWithDbConnection(
   DatabaseExecutor connection,
   List<String> radicals,

lib/search/word_search/word_search.dart

@@ -15,6 +15,7 @@ import 'package:sqflite_common/sqlite_api.dart';
 
 enum SearchMode { Auto, English, Kanji, MixedKanji, Kana, MixedKana }
 
+/// Searches for an input string, returning a list of results with their details. Returns null if the input string is empty.
 Future<List<WordSearchResult>?> searchWordWithDbConnection(
   DatabaseExecutor connection,
   String word, {
@@ -54,6 +55,7 @@ Future<List<WordSearchResult>?> searchWordWithDbConnection(
   return result;
 }
 
+/// Searches for an input string, returning the amount of results that the search would yield without pagination.
 Future<int?> searchWordCountWithDbConnection(
   DatabaseExecutor connection,
   String word, {
@@ -72,6 +74,7 @@ Future<int?> searchWordCountWithDbConnection(
   return entryIdCount;
 }
 
+/// Fetches a single word by its entry ID, returning null if not found.
 Future<WordSearchResult?> getWordByIdWithDbConnection(
   DatabaseExecutor connection,
   int id,
@@ -107,6 +110,7 @@ Future<WordSearchResult?> getWordByIdWithDbConnection(
   return result.firstOrNull;
 }
 
+/// Fetches multiple words by their entry IDs, returning a map from entry ID to result.
 Future<Map<int, WordSearchResult>> getWordsByIdsWithDbConnection(
   DatabaseExecutor connection,
   Set<int> ids,