chore: align Dart SDK minimum version to >=3.3.0 across all packages (#1343)

Update postgrest, realtime_client, storage_client, and functions_client
to require sdk: '>=3.3.0 <4.0.0', matching supabase_flutter, supabase,
and gotrue. Since supabase_flutter already requires Dart 3.3.0+,
advertising >=3.0.0 on sub-packages was misleading.

Remove redundant null assertion operators in postgrest_builder.dart
that become unnecessary_non_null_assertion warnings under Dart 3.3.0+
flow analysis.

Linear: SDK-814

Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: grdsdev

packages/functions_client/pubspec.yaml

@@ -6,7 +6,7 @@ repository: 'https://github.com/supabase/supabase-flutter/tree/main/packages/fun
 documentation: 'https://supabase.com/docs/reference/dart/functions-invoke'
 
 environment:
-  sdk: '>=3.0.0 <4.0.0'
+  sdk: '>=3.3.0 <4.0.0'
 
 dependencies:
   http: '>=0.13.4 <2.0.0'

packages/postgrest/lib/src/postgrest_builder.dart

@@ -107,9 +107,9 @@ class PostgrestBuilder<T, S, R> implements Future<T> {
     if (_count != null) {
       if (_headers['Prefer'] != null) {
         final oldPreferHeader = _headers['Prefer'];
-        _headers['Prefer'] = '$oldPreferHeader,count=${_count!.name}';
+        _headers['Prefer'] = '$oldPreferHeader,count=${_count.name}';
       } else {
-        _headers['Prefer'] = 'count=${_count!.name}';
+        _headers['Prefer'] = 'count=${_count.name}';
       }
     }
 
@@ -126,9 +126,9 @@ class PostgrestBuilder<T, S, R> implements Future<T> {
       if (_schema == null) {
         // skip
       } else if ([METHOD_GET, METHOD_HEAD].contains(method)) {
-        _headers['Accept-Profile'] = _schema!;
+        _headers['Accept-Profile'] = _schema;
       } else {
-        _headers['Content-Profile'] = _schema!;
+        _headers['Content-Profile'] = _schema;
       }
       if (method != METHOD_GET && method != METHOD_HEAD) {
         _headers['Content-Type'] = 'application/json';
@@ -194,7 +194,7 @@ class PostgrestBuilder<T, S, R> implements Future<T> {
         } else {
           try {
             if ((response.contentLength ?? 0) > 10000 && _isolate != null) {
-              body = await _isolate!.decode(response.body);
+              body = await _isolate.decode(response.body);
             } else {
               body = jsonDecode(response.body);
             }
@@ -249,7 +249,7 @@ class PostgrestBuilder<T, S, R> implements Future<T> {
       body as R;
 
       if (_converter != null) {
-        converted = _converter!(body);
+        converted = _converter(body);
       } else {
         converted = body as S;
       }
@@ -311,14 +311,14 @@ class PostgrestBuilder<T, S, R> implements Future<T> {
         error.details.toString().contains('Results contain 0 rows')) {
       if (_count != null && response.request!.method != METHOD_HEAD) {
         if (_converter != null) {
-          return PostgrestResponse<S>(data: _converter!(null as R), count: 0)
+          return PostgrestResponse<S>(data: _converter(null as R), count: 0)
               as T;
         } else {
           return null as T;
         }
       } else {
         if (_converter != null) {
-          return _converter!(null as R) as T;
+          return _converter(null as R) as T;
         } else {
           return null as T;
         }

packages/postgrest/pubspec.yaml

@@ -6,7 +6,7 @@ repository: 'https://github.com/supabase/supabase-flutter/tree/main/packages/pos
 documentation: 'https://supabase.com/docs/reference/dart/select'
 
 environment:
-  sdk: '>=3.0.0 <4.0.0'
+  sdk: '>=3.3.0 <4.0.0'
 
 dependencies:
   http: '>=0.13.0 <2.0.0'

packages/realtime_client/pubspec.yaml

@@ -6,7 +6,7 @@ repository: 'https://github.com/supabase/supabase-flutter/tree/main/packages/rea
 documentation: 'https://supabase.com/docs/reference/dart/subscribe'
 
 environment:
-  sdk: '>=3.0.0 <4.0.0'
+  sdk: '>=3.3.0 <4.0.0'
 
 dependencies:
   collection: ^1.15.0

packages/storage_client/pubspec.yaml

@@ -6,7 +6,7 @@ repository: 'https://github.com/supabase/supabase-flutter/tree/main/packages/sto
 documentation: 'https://supabase.com/docs/reference/dart/storage-createbucket'
 
 environment:
-  sdk: '>=3.0.0 <4.0.0'
+  sdk: '>=3.3.0 <4.0.0'
 
 dependencies:
   http: '>=0.13.4 <2.0.0'