feat: Add support for stargazer count and history

[ninadsutrave]

Fixes #4610

Adds the stargazer count and star history endpoints to ActivityService, next to the existing ListStargazers in activity_star.go:

• GetStargazerCount (GET /repos/{owner}/{repo}/stargazers/count)
• ListStargazerHistory (GET /repos/{owner}/{repo}/stargazers/history)

StargazerHistory.Week uses Timestamp, since the API returns it as a Unix timestamp, same as WeeklyCommitActivity. Accessors and the ListStargazerHistoryIter iterator are generated.

I used an AI assistant while working on this, and I've reviewed and tested the code myself.

[google-cla]

Thanks for your pull request! It looks like this may be your first contribution to a Google open source project. Before we can look at your pull request, you'll need to sign a Contributor License Agreement (CLA).

View this failed invocation of the CLA check for more information.

For the most up to date status, view the checks section at the bottom of the pull request.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.62%. Comparing base (e754d2c) to head (628a2f5).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #4611   +/-   ##
=======================================
  Coverage   98.61%   98.62%           
=======================================
  Files         199      199           
  Lines       18693    18729   +36     
=======================================
+ Hits        18435    18471   +36     
  Misses        258      258           

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[gmlewis]

Closing and reopening to kickstart the Google CLA check.

[ninadsutrave]

@gmlewis thanks for kicking it earlier. I've signed the CLA now, but cla/google has been stuck in progress since I reopened the PR. Could you re-run it when you get a chance?

[gmlewis]

@gmlewis thanks for kicking it earlier. I've signed the CLA now, but cla/google has been stuck in progress since I reopened the PR. Could you re-run it when you get a chance?

Unfortunately, it looks like it is having some problems right now. My kicking it didn't seem to help any. ☹️

[ninadsutrave]

@gmlewis the CLA check passes now after a push. Thanks for looking into it earlier!

[gmlewis]

Thank you, @ninadsutrave!
LGTM.
Awaiting second LGTM+Approval from any other contributor to this repo before merging.

cc: @stevehipwell - @Not-Dhananjay-Mishra

[Not-Dhananjay-Mishra]

We only write _Marshal tests for structs that implement custom Unmarshal/Marshal logic.
#4253 (comment)

Suggested change

	func TestStargazerCount_Marshal(t *testing.T) {
	t.Parallel()
	testJSONMarshal(t, &StargazerCount{}, `{"count":0}`)
	u := &StargazerCount{Count: 42}
	want := `{"count":42}`
	testJSONMarshal(t, u, want)
	}
	func TestStargazerHistory_Marshal(t *testing.T) {
	t.Parallel()
	u := &StargazerHistory{
	Days: []int{0, 12, 7, 0, 0, 0, 0},
	Total: 19,
	Week: referenceTimestamp,
	}
	want := `{
	"days": [0, 12, 7, 0, 0, 0, 0],
	"total": 19,
	"week": ` + referenceTimeStr + `
	}`
	testJSONMarshal(t, u, want)
	}