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 71.17%. Comparing base (8f76df9) to head (59168bd).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #505      +/-   ##
==========================================
+ Coverage   71.16%   71.17%   +0.01%     
==========================================
  Files         222      222              
  Lines       18684    18678       -6     
==========================================
- Hits        13296    13294       -2     
+ Misses       4204     4201       -3     
+ Partials     1184     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]

@srtaalej LGTM! Thanks for making those changes. I'm finding the following outputs in verbose logs for both endpoints with a ROSI app:

HTTP Request: POST https://slack.com/api/apps.hosted.icon HTTP/1.1
HTTP Request User-Agent: slack-cli/v4.0.1-ale-upload-icon-7-g59168bd (os: darwin)
HTTP Request Body: <binary image data, 265734 bytes>
HTTP Response Status: HTTP/1.1 200 OK
HTTP Response Body:
{"ok":true}

HTTP Request: POST https://slack.com/api/apps.icon.set HTTP/1.1
HTTP Request User-Agent: slack-cli/v4.0.1-ale-upload-icon-7-g59168bd (os: darwin)
HTTP Request Body: <binary image data, 265734 bytes>
HTTP Response Status: HTTP/1.1 200 OK
HTTP Response Body:
{"ok":true}