feat: add debug logging and retry support to icon upload

[srtaalej]

Changelog

Add verbose debug logging and retry support to icon upload API calls.

Summary

This PR refactors uploadIcon to use DoWithRetry instead of calling httpClient.Do directly, matching the pattern used by all other API methods. It adds verbose debug logging for icon upload requests and responses and automatic retry on rate limits for icon uploads

Addresses review feedback from #469 (comment)

Test plan

• go test ./internal/api/ -run Icon passes
• make build then slack run -e set-icon --verbose from a project with icon.png — confirm
  HTTP request/response details appear in verbose logs without binary noise

Requirements

• I've read and understood the Contributing Guidelines and have done my best effort to follow them.
• I've read and agree to the Code of Conduct.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 71.16%. Comparing base (5ffec6b) to head (560402d).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #505      +/-   ##
==========================================
- Coverage   71.17%   71.16%   -0.02%     
==========================================
  Files         222      222              
  Lines       18684    18680       -4     
==========================================
- Hits        13299    13294       -5     
  Misses       4203     4203              
- Partials     1182     1183       +1     

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[zimeg]

@srtaalej Super nice improvements to help troubleshooting! 📫

I'm hoping we can land a change or two more before this merges. One is in comments below but also I think we can remove these logs from output now too:

slack-cli/internal/pkg/apps/install.go

Line 534 in 560402d

clients.IO.PrintDebug(ctx, "uploading icon")

slack-cli/internal/pkg/apps/install.go

Line 659 in 560402d

clients.IO.PrintDebug(ctx, "uploading icon")

[zimeg]

Suggested change

	c.io.PrintDebug(ctx, "HTTP Request: %v %v", request.Method, request.URL)
	c.io.PrintDebug(ctx, "HTTP Request: %v %v %v", request.Method, request.URL, request.Proto)

🔭 suggestion: To match the entire request signature:

HTTP Request: POST https://slack.com/api/apps.icon.set HTTP/1.1