Fix httpx is not encoding with symbol '%s' (encode#3140)

Add parsing symbol '%s' test

rewrite fn::_urlparse::is_safe

httpx/_urlparse.py

@@ -424,13 +424,13 @@ def is_safe(string: str, safe: str = "/") -> bool:
     """
     Determine if a given string is already quote-safe.
     """
-    NON_ESCAPED_CHARS = UNRESERVED_CHARACTERS + safe + "%"
-
-    # All characters must already be non-escaping or '%'
-    for char in string:
-        if char not in NON_ESCAPED_CHARS:
+    NON_ESCAPED_CHARS = UNRESERVED_CHARACTERS + safe
+    # All characters must already be non-escaping or valid percent-encoded
+    for index, char in enumerate(string):
+        if char not in NON_ESCAPED_CHARS and not PERCENT_ENCODED_REGEX.match(
+            string[index : index + 3]
+        ):
             return False
-
     return True
 
 

tests/models/test_url.py

@@ -284,6 +284,8 @@ def test_url_leading_dot_prefix_on_relative_url():
 def test_param_requires_encoding():
     url = httpx.URL("http://webservice", params={"u": "with spaces"})
     assert str(url) == "http://webservice?u=with%20spaces"
+    url = httpx.URL("http://webservice", params={"u": "%"})
+    assert str(url) == "http://webservice?u=%25"
 
 
 def test_param_does_not_require_encoding():