fix(fetch): update to httpx 0.28+ proxy parameter

The httpx library renamed 'proxies' to 'proxy' in version 0.28.0.
This updates the fetch server to use the new parameter name and
removes the version cap on httpx.

Fixes #3287

src/fetch/pyproject.toml

@@ -16,7 +16,7 @@ classifiers = [
     "Programming Language :: Python :: 3.10",
 ]
 dependencies = [
-    "httpx<0.28",
+    "httpx>=0.27",
     "markdownify>=0.13.1",
     "mcp>=1.1.3",
     "protego>=0.3.1",

src/fetch/src/mcp_server_fetch/server.py

@@ -72,7 +72,7 @@ async def check_may_autonomously_fetch_url(url: str, user_agent: str, proxy_url:
 
     robot_txt_url = get_robots_txt_url(url)
 
-    async with AsyncClient(proxies=proxy_url) as client:
+    async with AsyncClient(proxy=proxy_url) as client:
         try:
             response = await client.get(
                 robot_txt_url,
@@ -116,7 +116,7 @@ async def fetch_url(
     """
     from httpx import AsyncClient, HTTPError
 
-    async with AsyncClient(proxies=proxy_url) as client:
+    async with AsyncClient(proxy=proxy_url) as client:
         try:
             response = await client.get(
                 url,

src/fetch/tests/test_server.py

@@ -323,4 +323,4 @@ class TestFetchUrl:
             )
 
             # Verify AsyncClient was called with proxy
-            mock_client_class.assert_called_once_with(proxies="http://proxy.example.com:8080")
+            mock_client_class.assert_called_once_with(proxy="http://proxy.example.com:8080")