feat: add --batch-size flag to push refs in batches (#173)

* feat: add --batch-size flag to push refs in batches

Add support for pushing refs in smaller batches to avoid server-side
limits and timeouts when syncing large repositories with many tags/branches.

- Add --batch-size flag (default 0 = no batching, original behavior)
- Add References() method to GitRepository interface
- Implement collectRefs() and pushRefsInBatches() helpers
- Add MinBatchSize validation (must be 0 or >= 10)

This addresses issues where repositories with 1000+ refs fail to sync
to GHES with 'command error on refs/heads/<branch>: failed' errors.

* test: add tests for batch-size flag and push batching functionality

* fix: pin tool dependencies to versions compatible with Go 1.21

* ci: fix docker compose v2 syntax and update setup-ruby action

* refactor: address PR review feedback

- Remove unused RefInfo struct from git.go
- Remove redundant pushedAny variable tracking in pushRefsInBatches
- Remove incomplete TestPushRefsInBatches_PartialUpToDate test (already covered by existing test case)

* docs: add --batch-size flag to README

script/bootstrap

@@ -18,12 +18,12 @@ if [ ! -f go.mod ]; then
     go mod init tools
 fi
 
-go get golang.org/x/tools/go/packages@master
+go get golang.org/x/tools/go/packages@v0.16.0
 
 if [ ! -f "${GOBIN}/mockgen" ]; then
     echo "mockgen was not found, installing..."
-    go get github.com/golang/mock/gomock@master
-    go get github.com/golang/mock/mockgen@master
+    go get github.com/golang/mock/gomock@v1.6.0
+    go get github.com/golang/mock/mockgen@v1.6.0
 fi
 
 if [ ! -f "${GOBIN}/golangci-lint" ]; then
@@ -33,5 +33,5 @@ fi
 
 if [ ! -f "${GOBIN}/goimports" ]; then
     echo "goimports was not found, installing..."
-    go get golang.org/x/tools/cmd/goimports@master
+    go get golang.org/x/tools/cmd/goimports@v0.16.0
 fi