Enable and fix non_constant_identifier_names lint (#407)

diff --git a/analysis_options.yaml b/analysis_options.yaml
index 9dfba69..462c5eb 100644
--- a/analysis_options.yaml
+++ b/analysis_options.yaml

@@ -44,6 +44,7 @@
     - implementation_imports
     - library_names
     - library_prefixes
+    - no_leading_underscores_for_local_identifiers
     - non_constant_identifier_names
     # - one_member_abstracts
     # - only_throw_errors

diff --git a/lib/src/hitmap.dart b/lib/src/hitmap.dart
index a80c8f2..326dfa1 100644
--- a/lib/src/hitmap.dart
+++ b/lib/src/hitmap.dart

@@ -99,7 +99,7 @@
       final ignoredLines = ignoredLinesList.iterator;
       var hasCurrent = ignoredLines.moveNext();
 
-      bool _shouldIgnoreLine(Iterator<List<int>> ignoredRanges, int line) {
+      bool shouldIgnoreLine(Iterator<List<int>> ignoredRanges, int line) {
         if (!hasCurrent || ignoredRanges.current.isEmpty) {
           return false;
         }
@@ -138,7 +138,7 @@
           final k = hits[i];
           if (k is int) {
             // Single line.
-            if (_shouldIgnoreLine(ignoredLines, k)) continue;
+            if (shouldIgnoreLine(ignoredLines, k)) continue;
 
             addToMap(hitMap, k, hits[i + 1] as int);
           } else if (k is String) {
@@ -147,7 +147,7 @@
             final start = int.parse(k.substring(0, splitPos));
             final end = int.parse(k.substring(splitPos + 1));
             for (var j = start; j <= end; j++) {
-              if (_shouldIgnoreLine(ignoredLines, j)) continue;
+              if (shouldIgnoreLine(ignoredLines, j)) continue;
 
               addToMap(hitMap, j, hits[i + 1] as int);
             }

diff --git a/lib/src/resolver.dart b/lib/src/resolver.dart
index 9b0e902..d2e799c 100644
--- a/lib/src/resolver.dart
+++ b/lib/src/resolver.dart

@@ -77,13 +77,13 @@
       return resolveSymbolicLinks(filePath);
     }
     if (uri.scheme == 'package') {
-      final _packages = this._packages;
-      if (_packages == null) {
+      final packages = _packages;
+      if (packages == null) {
         return null;
       }
 
       final packageName = uri.pathSegments[0];
-      final packageUri = _packages[packageName];
+      final packageUri = packages[packageName];
       if (packageUri == null) {
         failed.add('$uri');
         return null;

diff --git a/lib/src/util.dart b/lib/src/util.dart
index a85de49..dd379ae 100644
--- a/lib/src/util.dart
+++ b/lib/src/util.dart

@@ -13,7 +13,7 @@
     {Duration? timeout}) async {
   var keepGoing = true;
 
-  Future<dynamic> _withTimeout(Future Function() f, {Duration? duration}) {
+  Future<dynamic> withTimeout(Future Function() f, {Duration? duration}) {
     if (duration == null) {
       return f();
     }
@@ -27,7 +27,7 @@
     });
   }
 
-  return _withTimeout(() async {
+  return withTimeout(() async {
     while (keepGoing) {
       try {
         return await f();

diff --git a/test/lcov_test.dart b/test/lcov_test.dart
index 773c46c..59ff38c 100644
--- a/test/lcov_test.dart
+++ b/test/lcov_test.dart

@@ -154,7 +154,7 @@
       // be very careful if you change the test file
       expect(res, contains('      0|  return a - b;'));
 
-      expect(res, contains('|  return _withTimeout(() async {'),
+      expect(res, contains('|  return withTimeout(() async {'),
           reason: 'be careful if you change lib/src/util.dart');
 
       final hitLineRegexp = RegExp(r'\s+(\d+)\|  return a \+ b;');
@@ -177,7 +177,7 @@
       // be very careful if you change the test file
       expect(res, contains('      0|  return a - b;'));
 
-      expect(res, contains('|  return _withTimeout(() async {'),
+      expect(res, contains('|  return withTimeout(() async {'),
           reason: 'be careful if you change lib/src/util.dart');
 
       final hitLineRegexp = RegExp(r'\s+(\d+)\|  return a \+ b;');