Allow ParamMethod and ParamFunction to be lazy

[philippjfr]

No description provided.

[codecov]

Codecov Report

Merging #1966 (6ab689e) into master (c173b5d) will decrease coverage by 0.00%.
The diff coverage is 88.23%.

@@            Coverage Diff             @@
##           master    #1966      +/-   ##
==========================================
- Coverage   84.84%   84.83%   -0.01%     
==========================================
  Files         166      166              
  Lines       20032    20035       +3     
==========================================
+ Hits        16996    16997       +1     
- Misses       3036     3038       +2     

Impacted Files	Coverage Δ
panel/param.py	89.21% <88.23%> (+0.06%)	⬆️
panel/io/reload.py	65.88% <0.00%> (-2.36%)	⬇️

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