remove http timeout (#7291)

## Problem

https://github.com/neondatabase/cloud/issues/11051

additionally, I felt like the http logic was a bit complex.

## Summary of changes

1. Removes timeout for HTTP requests.
2. Split out header parsing to a `HttpHeaders` type.
3. Moved db client handling to `QueryData::process` and
`BatchQueryData::process` to simplify the logic of `handle_inner` a bit.

test_runner/regress/test_proxy.py

@@ -566,38 +566,6 @@ async def test_sql_over_http2(static_proxy: NeonProxy):
     assert resp["rows"] == [{"answer": 42}]
 
 
-def test_sql_over_http_timeout_cancel(static_proxy: NeonProxy):
-    static_proxy.safe_psql("create role http with login password 'http' superuser")
-
-    static_proxy.safe_psql("create table test_table ( id int primary key )")
-
-    # insert into a table, with a unique constraint, after sleeping for n seconds
-    query = "WITH temp AS ( \
-        SELECT pg_sleep($1) as sleep, $2::int as id \
-    ) INSERT INTO test_table (id) SELECT id FROM temp"
-
-    # expect to fail with timeout
-    res = static_proxy.http_query(
-        query,
-        [static_proxy.http_timeout_seconds + 1, 1],
-        user="http",
-        password="http",
-        expected_code=400,
-    )
-    assert "Query cancelled, runtime exceeded" in res["message"], "HTTP query should time out"
-
-    time.sleep(2)
-
-    res = static_proxy.http_query(query, [1, 1], user="http", password="http", expected_code=200)
-    assert res["command"] == "INSERT", "HTTP query should insert"
-    assert res["rowCount"] == 1, "HTTP query should insert"
-
-    res = static_proxy.http_query(query, [0, 1], user="http", password="http", expected_code=400)
-    assert (
-        "duplicate key value violates unique constraint" in res["message"]
-    ), "HTTP query should conflict"
-
-
 def test_sql_over_http_connection_cancel(static_proxy: NeonProxy):
     static_proxy.safe_psql("create role http with login password 'http' superuser")