Defer import of requests and urllib

This saves 100ms-150ms of startup time on "from pwn import *"

pwn/toplevel.py

@@ -6,7 +6,6 @@
 import os
 import platform
 import re
-import requests
 import socks
 import signal
 import string

pwnlib/libcdb.py

@@ -7,11 +7,8 @@
 import codecs
 import json
 import os
-import requests
 import tempfile
 
-from six.moves import urllib
-
 from pwnlib.context import context
 from pwnlib.elf import ELF
 from pwnlib.log import getLogger
@@ -29,6 +26,10 @@
 # https://gitlab.com/libcdb/libcdb wasn't updated after 2019,
 # but still is a massive database of older libc binaries.
 def provider_libcdb(hex_encoded_id, hash_type):
+    # Deferred import because it's slow
+    import requests
+    from six.moves import urllib
+
     # Build the URL using the requested hash type
     url_base = "https://gitlab.com/libcdb/libcdb/raw/master/hashes/%s/" % hash_type
     url      = urllib.parse.urljoin(url_base, hex_encoded_id)
@@ -53,6 +54,9 @@ def provider_libcdb(hex_encoded_id, hash_type):
 
 # https://libc.rip/
 def provider_libc_rip(hex_encoded_id, hash_type):
+    # Deferred import because it's slow
+    import requests
+
     # Build the request for the hash type
     # https://github.com/niklasb/libc-database/blob/master/searchengine/api.yml
     if hash_type == 'build_id':