viz, vizspec, advn

[OutOfBedlam]

This pull request introduces new functionality and tests for the advn package, focusing on improved JSON marshaling/unmarshaling, time formatting options, and expanded test coverage for ECharts and PNG output. The changes add robust JSON handling, flexible output time formatting, and comprehensive tests for ECharts and PNG rendering logic.

New Features and Enhancements:

• Added custom JSON marshaling and unmarshaling implementations for Spec, Series, and Domain, along with utility functions for parsing and validating JSON input (jsh/advn/json.go).
• Introduced OutputTimeOptions and related logic for formatting and encoding time values with support for time zones and multiple formats, improving ECharts output flexibility (jsh/advn/output_time.go).

Testing Improvements:

• Added extensive unit tests for ECharts option generation, covering band, histogram, boxplot, event series, unsupported representations, and time formatting overrides (jsh/advn/echarts_test.go).
• Introduced tests for PNG legend and layout planning, ensuring correct behavior for legend rendering under various conditions (jsh/advn/png_test.go).

Dependency Updates:

• Promoted golang.org/x/image from an indirect to a direct dependency in go.mod to support new image processing requirements. [1] [2]

[codecov]

Codecov Report

❌ Patch coverage is 66.64556% with 1580 lines in your changes missing coverage. Please review.
✅ Project coverage is 48.39%. Comparing base (3584b6c) to head (76892b7).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
jsh/advn/svg.go	75.97%	223 Missing and 109 partials ⚠️
jsh/advn/png.go	62.67%	254 Missing and 70 partials ⚠️
jsh/advn/echarts.go	61.21%	177 Missing and 53 partials ⚠️
jsh/advn/tui.go	62.76%	163 Missing and 66 partials ⚠️
jsh/advn/time.go	34.78%	134 Missing and 16 partials ⚠️
jsh/lib/vizspec/vizspec.go	59.29%	52 Missing and 40 partials ⚠️
jsh/advn/validate.go	70.76%	51 Missing and 18 partials ⚠️
jsh/advn/output_time.go	40.40%	51 Missing and 8 partials ⚠️
jsh/lib/shell/expand.go	71.77%	27 Missing and 19 partials ⚠️
jsh/advn/json.go	84.87%	10 Missing and 8 partials ⚠️
... and 4 more

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #361      +/-   ##
==========================================
+ Coverage   47.30%   48.39%   +1.08%     
==========================================
  Files         327      338      +11     
  Lines       58572    63251    +4679     
==========================================
+ Hits        27710    30608    +2898     
- Misses      27804    29202    +1398     
- Partials     3058     3441     +383     

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