Change from %r to %s for NumPy 2.0 compatibility

[orthorhombic]

Fixes #3352

Summary/Motivation:

This changes %r to %s in the nl_writer for NumPy 2.0 compatibility. I believe this was missed in #3292

Changes proposed in this PR:

const = 'n%r\n' gets changed to const = 'n%s\n'

Legal Acknowledgement

By contributing to this software project, I have read the contribution guide and agree to the following terms and conditions for my contribution:

1. I agree my contributions are submitted under the BSD license.
2. I represent I am authorized to make the contributions and grant the license. If my employer has rights to intellectual property that includes these contributions, I represent that I have received permission to make contributions and grant the required license on behalf of that employer.

[orthorhombic]

@mrmundt & @jsiirola - Just figured I'd tag you here for awareness based on your work with #3292

[mrmundt]

Thanks, @orthorhombic ! Could you do me a favor and add a small test that ensures the right behavior is happening? Tests for the NL writer can be found in: https://github.com/Pyomo/pyomo/tree/main/pyomo/repn/tests/ampl <- most likely the test_nlv2.py file would be the best bet, but do what feels right.

If you need help, let us know.

[jsiirola]

@orthorhombic: Thank you for catching & resolving this! This is an important catch / fix ... I took the liberty of resolving a merge conflict and adding a test so that we can get this reviewed and merged for the next release (tomorrow!!).

[jsiirola]

Approved, pending successful tests.

[orthorhombic]

Sorry I'm just catching up on messages here. Thanks for the quick turnaround, and that this could make it into the next release!

If anything comes up, I can take a look a bit later.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 88.60%. Comparing base (ccc96bf) to head (f3a07ed).
Report is 109 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3353   +/-   ##
=======================================
  Coverage   88.59%   88.60%           
=======================================
  Files         874      874           
  Lines       99124    99124           
=======================================
+ Hits        87822    87831    +9     
+ Misses      11302    11293    -9     

Flag	Coverage Δ
linux	86.13% <100.00%> (ø)
osx	75.80% <100.00%> (ø)
other	86.64% <100.00%> (+<0.01%)	⬆️
win	83.96% <100.00%> (+0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.