Organize the code in client/cas.go (#424)

[`go/pkg/client/cas.go`](https://github.com/bazelbuild/remote-apis-sdks/blob/e62cf9b8696a2316c50ffe69bafe0a7972bcddff/go/pkg/client/cas.go)
was approaching the 2k lines mark with 95 symbols. Split the file into two, one
for upload behaviour and one for download behaviour.

This PR has no functional changes.

Tested by successfully running `bazel build //...`.

This is a pre-work for merging in
[`go/pkg/cas/`](https://github.com/bazelbuild/remote-apis-sdks/tree/e62cf9b8696a2316c50ffe69bafe0a7972bcddff/go/pkg/cas).
4 files changed
tree: b157e2a9cd3aac6ad1081e753bd53b43d2be96e6
  1. .bazelci/
  2. .githooks/
  3. .github/
  4. external/
  5. go/
  6. .gitignore
  7. .golangci.yml
  8. AUTHORS
  9. BUILD.bazel
  10. check-gofmt.sh
  11. check-golint.sh
  12. CONTRIBUTING.md
  13. CONTRIBUTORS
  14. go.mod
  15. go.sum
  16. LICENSE
  17. README.md
  18. remote-apis-sdks-deps.bzl
  19. setup-githooks.sh
  20. WORKSPACE
README.md

Remote Execution API SDKs

CI status: Build Status

PkgGoDev

This repository contains SDKs for the Remote Execution API.

See each language subdirectory's README.md for more specific instructions on using the SDK for that language.