wip: add event attachment download support

[seanhoughton]

Attachments can be listed and downloaded. Text attachments are returned inline with the text response. Binary attachments are included as embedded resource.

This is a prototype implementation to address my feature request: #314. It works very well for small-ish text attachments. I think we should consider a size limit and just return the download URL for anything larger than that limit.

I'm also wondering of we should detect image types and return them as type: "image" content blocks.

I've discovered that VSCode does allow you to download embedded resources, but it's a tiny button that's hidden unless you expand the results of a tool execution. It does not allow you to save the resource to disk as part of the chat.

[codecov]

Codecov Report

Attention: Patch coverage is 38.39286% with 138 lines in your changes missing coverage. Please review.

Project coverage is 58.32%. Comparing base (801f2e6) to head (6b909e5).
Report is 8 commits behind head on main.

Files with missing lines	Patch %	Lines
packages/mcp-server/src/tools.ts	30.20%	67 Missing ⚠️
packages/mcp-server/src/api-client/client.ts	3.50%	55 Missing ⚠️
packages/mcp-server/src/server.ts	0.00%	16 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #346      +/-   ##
==========================================
- Coverage   59.37%   58.32%   -1.05%     
==========================================
  Files          49       49              
  Lines        6038     6263     +225     
  Branches      472      470       -2     
==========================================
+ Hits         3585     3653      +68     
- Misses       2453     2610     +157     

Flag	Coverage Δ
unittests	58.32% <38.39%> (-1.05%)	⬇️

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[seanhoughton]

The initial PR was pretty rough so I've made a few improvements in the code structure and added support for ImageContent responses. VSCode handles images and binary data and lets you save the files manually - it's not the greatest user experience, but once you learn where it is then it's not too bad.

[dcramer]

will work on getting this merged after i land #356

[dcramer]

Alright merged in #358. Thanks @seanhoughton!