fix/other: fix bug with network y-axis labels and cache height calculations

[ClementTsang]

Description

A description of the change, what it does, and why it was made. If relevant (such as any change that modifies the UI), please provide screenshots of the changes:

This PR has two changes:

1. Fix a bug where we were using the wrong value when creating network y-axis labels; this was a mistake from refactor: points rework (v1) #1663, where I used the upper limit (value * 1.5) as the value to create labels. Oops.
2. Cache previous results of height calculation; this means we don't have to always scan the full range of points each time we want to find the max height for the adjusting y-axis. Instead:
   • If the cache is empty, scan the full range; store the best point, the right edge scanned, and the time range
   • If the cache is not empty, and the point is inside the current range, scan from the right edge to the cached right edge
   • If the cache is not empty but the point is outside the range, scan the full thing as it's invalid
   • If the cache is not empty but the time range is different, we do the easy thing and just scan the entire thing again too

Issue

If applicable, what issue does this address?

Closes: #

Testing

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If this is a code change, please also indicate which platforms were tested:

• Windows
• macOS
• Linux

Checklist

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• Areas your change affects have been linted using rustfmt (cargo fmt)
• The change has been tested and doesn't appear to cause any unintended breakage
• Documentation has been added/updated if needed (README.md, help menu, doc pages, etc.)
• The pull request passes the provided CI pipeline
• There are no merge conflicts
• If relevant, new tests were added (don't worry too much about coverage)

[codecov]

Codecov Report

Attention: Patch coverage is 3.22581% with 30 lines in your changes missing coverage. Please review.

Project coverage is 42.13%. Comparing base (8ac03b5) to head (a11285e).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/canvas/widgets/network_graph.rs	0.00%	30 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1670      +/-   ##
==========================================
- Coverage   42.25%   42.13%   -0.12%     
==========================================
  Files         110      110              
  Lines       17458    17478      +20     
==========================================
- Hits         7377     7365      -12     
- Misses      10081    10113      +32     

Flag	Coverage Δ
macos-14	37.79% <3.22%> (-0.05%)	⬇️
ubuntu-latest	43.91% <3.22%> (-0.13%)	⬇️
windows-2019	37.68% <3.22%> (-0.05%)	⬇️

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