allow one-sided limit in scale_*_tint_*()

[Fan-iX]

Allowing limits=c(lower_limit, NA) or limits=c(NA, upper_limit) in scale_*_tint_*() functions.

For example, scale_fill_hypso_tint_c("gmt_globe", limits=c(0,NA)) will get the same effect as scale_fill_hypso_tint_c("gmt_globe_hypso")

[codecov]

Codecov Report

❌ Patch coverage is 0% with 24 lines in your changes missing coverage. Please review.
✅ Project coverage is 98.92%. Comparing base (7007704) to head (ad1c82f).
⚠️ Report is 52 commits behind head on main.

Files with missing lines	Patch %	Lines
R/scales_cross_blended.R	0.00%	8 Missing ⚠️
R/scales_grass.R	0.00%	8 Missing ⚠️
R/scales_hypso.R	0.00%	8 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #170      +/-   ##
==========================================
- Coverage   99.64%   98.92%   -0.72%     
==========================================
  Files          50       50              
  Lines        3340     3364      +24     
==========================================
  Hits         3328     3328              
- Misses         12       36      +24     

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