feat(gax): add ResumableUploadCallable and ResumableUploadCallSettings

[blakeli0]

Description

This PR introduces the foundational GAX Public API surface for HTTP/JSON resumable uploads.

Changes

1. ResumableUploadCallSettings: Non-generic @AutoValue configuration class with merge(other) method and chunkSize = 8MB default.
2. ResumableUploadCallable: Abstract transport-agnostic base class with a single futureCall(request, payload, settings) method.
3. ResumableUploadCallSettingsTest: JUnit 5 (Jupiter) unit tests verifying default chunk boundaries and merge(other) overrides.

[gemini-code-assist]

Code Review

This pull request introduces the ResumableUploadCallSettings and ResumableUploadCallable classes to support transport-independent resumable uploads, along with associated unit tests. The review feedback suggests adding input validation to ensure chunkSize is positive and totalBytes is non-negative, as well as removing several redundant null casts in the overloaded call and futureCall methods to clean up the code.

[gemini-code-assist]

It is highly recommended to validate that chunkSize is positive when it is configured. This prevents invalid configurations (such as negative or zero chunk sizes) from being set and causing runtime failures during uploads.

    public Builder<RequestT, ResponseT> setChunkSize(Integer chunkSize) {
      if (chunkSize != null) {
        com.google.common.base.Preconditions.checkArgument(
            chunkSize > 0, "chunkSize must be positive: %s", chunkSize);
      }
      this.chunkSize = chunkSize;
      return this;
    }

[gemini-code-assist]

It is highly recommended to validate that totalBytes is non-negative when configured. This prevents invalid negative values from being set.

    public Builder<RequestT, ResponseT> setTotalBytes(Long totalBytes) {
      if (totalBytes != null) {
        com.google.common.base.Preconditions.checkArgument(
            totalBytes >= 0, "totalBytes must be non-negative: %s", totalBytes);
      }
      this.totalBytes = totalBytes;
      return this;
    }

[gemini-code-assist]

The cast (ApiCallContext) null is redundant because there is only one 4-argument overload of futureCall, so the compiler can resolve the method call unambiguously. Removing the redundant cast improves code readability.

Suggested change

	public ApiFuture<ResponseT> futureCall(
	RequestT request,
	InputStream payload,
	ResumableUploadCallSettings<RequestT, ResponseT> perRequestSettings) {
	return futureCall(request, payload, perRequestSettings, (ApiCallContext) null);
	}
	public ApiFuture<ResponseT> futureCall(
	RequestT request,
	InputStream payload,
	ResumableUploadCallSettings<RequestT, ResponseT> perRequestSettings) {
	return futureCall(request, payload, perRequestSettings, null);
	}

[gemini-code-assist]

The casts (ResumableUploadCallSettings<RequestT, ResponseT>) null and (ApiCallContext) null are redundant because there is only one 4-argument overload of futureCall. Removing them simplifies the code and improves readability.

  public ApiFuture<ResponseT> futureCall(RequestT request, InputStream payload) {
    return futureCall(request, payload, null, null);
  }

[gemini-code-assist]

The cast (ApiCallContext) null is redundant because there is only one 4-argument overload of call. Removing it improves readability.

Suggested change

	public ResponseT call(
	RequestT request,
	InputStream payload,
	ResumableUploadCallSettings<RequestT, ResponseT> perRequestSettings) {
	return call(request, payload, perRequestSettings, (ApiCallContext) null);
	}
	public ResponseT call(
	RequestT request,
	InputStream payload,
	ResumableUploadCallSettings<RequestT, ResponseT> perRequestSettings) {
	return call(request, payload, perRequestSettings, null);
	}

[gemini-code-assist]

The casts (ResumableUploadCallSettings<RequestT, ResponseT>) null and (ApiCallContext) null are redundant because there is only one 4-argument overload of call. Removing them simplifies the code.

  public ResponseT call(RequestT request, InputStream payload) {
    return call(request, payload, null, null);
  }