fix: compress pipeline graphs before sending to mermaid

[lbux]

Related Issues

• fixes Mermaid Crashes If trying to draw a large pipeline #8089

Proposed Changes:

When pipelines get too big, the resulting base64 output is too long when we send a request to the mermaid server leading to a HTTP 400 error. Mermaid supports compressed URLS using Pako. With zlib, we are able to compress our input in the expected format and send it off to Mermaid.

How did you test it?

I wanted to do as close to a 1:1 change so that this has 0 impact to the user. The same tests were used which hopefully means the changes are 1:1 as they have all passed.

I am also asking for tests from Haystack users with big pipelines on Discord.

Notes for the reviewer

I will make another PR that will use this change as a foundation for:

• Extension parameters (jpg, png, webp, svg, pdf)
• Background color modifications
• Themes
• Image size

Aaaaand.... offline support! #7896

Checklist

• I have read the contributors guidelines and the code of conduct
• I have updated the related issue with new insights and changes
• I added unit tests and updated the docstrings
• I've used one of the conventional commit types for my PR title: fix:, feat:, build:, chore:, ci:, docs:, style:, refactor:, perf:, test: and added ! in case the PR includes breaking changes.
• I documented my code
• I ran pre-commit hooks and fixed any issue

[coveralls]

Pull Request Test Coverage Report for Build 12944303830

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 2 unchanged lines in 1 file lost coverage.
• Overall coverage increased (+0.002%) to 91.338%

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Files with Coverage Reduction	New Missed Lines	%
core/pipeline/draw.py	2	97.1%

Totals
Change from base Build 12928411205:	0.002%
Covered Lines:	8858
Relevant Lines:	9698

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💛 - Coveralls