info: Parallelize repo info to improve performance

For a large checkout like chromiumos or android, `repo info` takes a
really long time! On my machine it took ~6 minutes. On a randomly
selected ChromiumOS cq-orchestrator build it took 4.1 minutes:
https://ci.chromium.org/b/8682060180498819729. This adds up to a lot of
wasted runtime for both humans and bots.

The problem is that `repo info` was single-threaded, which causes poor
performance when the checkout has 1000+ projects. We already have a
pattern for parallelization; let's use it.

BUG=None
TEST=Manually run, ensure no diff

Change-Id: I6b82b9495eb2a0e602a142dd3a16f09217871e1b
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/581921
Tested-by: Greg Edelston <gredelston@google.com>
Commit-Queue: Greg Edelston <gredelston@google.com>
Reviewed-by: Mike Frysinger <vapier@google.com>

man/repo-info.1

@@ -14,6 +14,10 @@ Get info on the manifest branch, current branch or unmerged branches
 \fB\-h\fR, \fB\-\-help\fR
 show this help message and exit
 .TP
+\fB\-j\fR JOBS, \fB\-\-jobs\fR=\fI\,JOBS\/\fR
+number of jobs to run in parallel (default: based on
+number of CPU cores)
+.TP
 \fB\-d\fR, \fB\-\-diff\fR
 show full info and commit diff including remote
 branches

man/repo-manifest.1

@@ -1,5 +1,5 @@
 .\" DO NOT MODIFY THIS FILE!  It was generated by help2man.
-.TH REPO "1" "April 2026" "repo manifest" "Repo Manual"
+.TH REPO "1" "May 2026" "repo manifest" "Repo Manual"
 .SH NAME
 repo \- repo manifest - manual page for repo manifest
 .SH SYNOPSIS
@@ -697,7 +697,7 @@ default to which all projects in the included manifest belong. This recurses,
 meaning it will apply to all projects in all manifests included as a result of
 this element.
 .PP
-Local Manifests
+Local Manifests 
 .PP
 Additional remotes and projects may be added through local manifest files stored
 in `$TOP_DIR/.repo/local_manifests/*.xml`.