Remove Dask dependency

Change clock to `time.monotonic()`, to prevent issues with clock
going backwards in some systems.

benchmarks/cudf-merge.py

@@ -9,15 +9,18 @@
 import os
 import pickle
 import pstats
-from time import perf_counter as clock
+from time import monotonic as clock
 
 import cupy
 import numpy as np
 
-from dask.utils import format_bytes, format_time
-
 import ucp
-from ucp._libs.utils import print_multi, print_separator
+from ucp._libs.utils import (
+    format_bytes,
+    format_time,
+    print_multi,
+    print_separator,
+)
 from ucp.utils import hmean, run_on_local_network
 
 # Must be set _before_ importing RAPIDS libraries (cuDF, RMM)

ucp/_libs/utils.py

@@ -13,9 +13,19 @@ def nvtx_annotate(message=None, color=None, domain=None):
 
 
 try:
-    from dask.utils import format_bytes, parse_bytes
+    from dask.utils import format_bytes, format_time, parse_bytes
 except ImportError:
 
+    def format_time(x):
+        if x < 1e-6:
+            return f"{x * 1e9:.3f} ns"
+        if x < 1e-3:
+            return f"{x * 1e6:.3f} us"
+        if x < 1:
+            return f"{x * 1e3:.3f} ms"
+        else:
+            return f"{x:.3f} s"
+
     def format_bytes(x):
         """Return formatted string in B, KiB, MiB, GiB or TiB"""
         if x < 1024: