implements biased IntegralArray for floats

[mleseach]

This PR fixes #18 by introducing a bias to improve numerical stability in IntegralArray computations.

For floating-point arrays, a bias equal to the mean of the array is applied automatically.

For non-floating types (e.g. integers), the bias is ignored and behavior is unchanged.

Implementation details:

• A new bias field is added to IntegralArray.
• Before integration, bias is added to every element of the array.
• During evaluation, bias * area is subtracted from the result.

Currently, the bias can't be easily specified by the user, as I'm not sure how best to handle cases where the bias type doesn't match the type of the array.
Let me know if you'd like any changes or additional tests.

[codecov]

Codecov Report

❌ Patch coverage is 94.44444% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 95.83%. Comparing base (33decc4) to head (9e66ec2).

Files with missing lines	Patch %	Lines
src/IntegralArrays.jl	94.44%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #22      +/-   ##
==========================================
- Coverage   97.29%   95.83%   -1.47%     
==========================================
  Files           1        1              
  Lines          37       48      +11     
==========================================
+ Hits           36       46      +10     
- Misses          1        2       +1     

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