add --workers option

Cargo.lock

@@ -481,7 +481,6 @@ dependencies = [
  "ctrlc",
  "fancy-regex",
  "num-integer",
- "num_cpus",
  "rpassword",
  "sequoia-openpgp",
 ]
@@ -605,12 +604,6 @@ version = "0.5.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "2304e00983f87ffb38b55b444b5e3b60a884b5d30c0fca7d82fe33449bbe55ea"
 
-[[package]]
-name = "hermit-abi"
-version = "0.5.2"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "fc0fef456e4baa96da950455cd02c081ca953b141298e41db3fc7e36b1da849c"
-
 [[package]]
 name = "iana-time-zone"
 version = "0.1.65"
@@ -994,16 +987,6 @@ dependencies = [
  "autocfg",
 ]
 
-[[package]]
-name = "num_cpus"
-version = "1.17.0"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "91df4bbde75afed763b708b7eee1e8e7651e02d97f6d5dd763e89367e957b23b"
-dependencies = [
- "hermit-abi",
- "libc",
-]
-
 [[package]]
 name = "objc2"
 version = "0.6.4"