Move bilinear import to avoid unnecessary warning

[yunjunz]

This PR moves the bilinear module import from the top of image.py to the function body of ImageContainerBilinear.resample().

conda install -c conda-forge pyresample does not install xarray and zarr. Thus, if one did not install xarray and zarr manually, running import pyresample will print out the following warning message:

(test) yunjunz:~>$ python -c "import pyresample"
/Users/yunjunz/tools/miniconda3/envs/test/lib/python3.10/site-packages/pyresample/bilinear/__init__.py:50: UserWarning: XArray and/or zarr not found, XArrayBilinearResampler won't be available.
  warnings.warn("XArray and/or zarr not found, XArrayBilinearResampler won't be available.")

With this change, the top-level import pyresample, which calls from pyresample import image, won't call the bilinear module, thus, avoid the warning msg.

• Closes Importing pyresample without having Xarray and/or zarray raises UserWarning #375
• Tests passed
• Passes git diff origin/main **/*py | flake8 --diff

[codecov]

Codecov Report

Merging #400 (1adca63) into main (e6a452e) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main     #400   +/-   ##
=======================================
  Coverage   93.81%   93.81%           
=======================================
  Files          65       65           
  Lines       11076    11077    +1     
=======================================
+ Hits        10391    10392    +1     
  Misses        685      685           

Flag	Coverage Δ
unittests	93.81% <100.00%> (+<0.01%)	⬆️

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

Impacted Files	Coverage Δ
pyresample/image.py	85.00% <100.00%> (+0.18%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update e6a452e...1adca63. Read the comment docs.

[coveralls]

Coverage increased (+0.0006%) to 93.62% when pulling 1adca63 on yunjunz:main into e6a452e on pytroll:main.

[djhoese]

Looks good. Thank you very much for clearing this up.