fix: display values for Y-axis when data points are all identical

[viiccwen]

Problem Description

When all data points in a series have identical values (e.g., [1, 1, 1, 1, 1]), the Y-axis would not display the correct value labels. This occurred because when the interval between minimum and maximum values is zero, the calculation for Y-axis labels would fail to produce meaningful output.

Issues

resolves #61

Root Cause

The issue was in the Y-axis label calculation logic in asciigraph.go. When interval = 0 (all data points are identical), the code would set ratio = 1 but the subsequent calculations for rows and Y-axis label positioning would not handle this edge case properly, resulting in missing or incorrect Y-axis values.

Fix Details

The fix ensures that when all data points are identical:

• The Y-axis properly displays the single value that all data points represent
• The graph maintains a minimum height to show the value clearly
• The axis labels are correctly positioned and formatted

Impact

• Y-axis now correctly displays values when all data points are identical
• Graphs with flat data (all same values) are now properly rendered
• Maintains backward compatibility for all other use cases
• Improves the visual representation of constant data series

I already asked about solving this in #61 comments~
If have any concerns, pls comment below! I'll reply ASAP.

[coveralls]

Pull Request Test Coverage Report for Build 16435238690

Details

• 3 of 3 (100.0%) changed or added relevant lines in 1 file are covered.
• 2 unchanged lines in 1 file lost coverage.
• Overall coverage decreased (-0.5%) to 95.561%

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Files with Coverage Reduction	New Missed Lines	%
asciigraph.go	2	99.05%

Totals
Change from base Build 11530076975:	-0.5%
Covered Lines:	366
Relevant Lines:	383

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💛 - Coveralls