Fix bugs in AstroCalc Planetary Transits

[worachate001]

Description

In AstroCalc/Eclipses & transits tool (in development). There are bugs in rare cases.

1. Partial/grazing transits that only visible in some parts of the world.
2. Transits that occur around sunset/sunrise. Observable duration becomes more complicate to compute in certain (small) area of visibility on Earth's surface.

This patch should give correct result for those scenarios.

Examples:

Geocentric

• No transit: 960 October 28 (but partial transit is visible in some parts of the world, Lat. +40, Long. -70, for example)
• Partial transit: 1342 October 21, 1937 May 11

Topocentric

• Total & partial transit: 1999 November 16 at Lat. 0, Long. +150 (total transit) / Lat. -60, Long. +150 (partial transit)
• No transit & partial transit: 1937 May 11 at Lat. +60, Long. 0 (no transit) / Lat. -30, Long. 0 (partial transit)
• Transit begins --> sunset --> sunrise --> transit ends: 2012 June 5/6 Lat. +60, Long. -20

I'll continue to test this tool to search for other potential bug.

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• This change requires a documentation update

How Has This Been Tested?

Test Configuration:

• Operating system: Windows 10
• Graphics Card: NVidia Geforce RTX

Checklist:

• My code follows the code style of this project.
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation (header file)
• I have updated the respective chapter in the Stellarium User Guide
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

[github-actions]

Great PR! Please pay attention to the following items before merging:

Files matching src/**/*.cpp:

• Are possibly unused includes removed?

This is an automatically generated QA checklist based on modified files

[alex-w]

Thank you!

[github-actions]

Hello @worachate001! Please check the fresh version (development snapshot) of Stellarium:
https://github.com/Stellarium/stellarium-data/releases/tag/weekly-snapshot

[github-actions]

Hello @worachate001! Please check the latest stable version of Stellarium:
https://github.com/Stellarium/stellarium/releases/latest