pathlog: increase fastlog batch size

Summary: I tried batch size 100, 1000 and 2000, seems the best value is 1000 based on my manual tests: running `sl log`  on `eden/scm/tests` folder.

Differential Revision: D83785298

fbshipit-source-id: 46f73cd11bd312a1e48406dc518b179a50319965

Author: zzl0

eden/scm/sapling/pathlog.py

@@ -15,7 +15,7 @@
 
 BATCH_SIZE = 500
 
-FASTLOG_BATCH_SIZE = 100
+FASTLOG_BATCH_SIZE = 1000
 FASTLOG_TIMEOUT = 50