Fix Fweights Bug in Poisson Regression

[s3alfisc]

• Fix Fweights Bug in Poisson Regression
• Adjust unit tests

[codecov]

Codecov Report

❌ Patch coverage is 87.50000% with 1 line in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
pyfixest/estimation/fepois_.py	66.66%	1 Missing ⚠️

Flag	Coverage Δ
core-tests	76.04% <87.50%> (+0.23%)	⬆️
tests-extended	?
tests-vs-r	16.12% <0.00%> (-0.02%)	⬇️

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

Files with missing lines	Coverage Δ
pyfixest/estimation/feols_.py	86.53% <100.00%> (-4.52%)	⬇️
pyfixest/estimation/fepois_.py	90.78% <66.66%> (+0.04%)	⬆️

... and 6 files with indirect coverage changes

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