fix: allow log tick labels below epsilon

[krystophny]

User description

Summary

• use machine epsilon when detecting zero in tick formatting utilities
• allow log tick labels to emit mathtext for arbitrarily small magnitudes

Testing

• make test

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PR Type

Bug fix

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Description

• Replace hardcoded epsilon with machine epsilon in tick formatting

• Fix zero detection for logarithmic tick labels

• Improve numerical precision for small magnitude values

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Diagram Walkthrough

flowchart LR
  A["Hardcoded epsilon (1.0e-10)"] --> B["Machine epsilon function"]
  B --> C["Improved zero detection"]
  C --> D["Better log tick formatting"]

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File Walkthrough

	Relevant files
Bug fix	fortplot_tick_formatting.f90 Replace hardcoded epsilon with machine epsilon                      src/utilities/ticks/fortplot_tick_formatting.f90 Replace hardcoded 1.0e-10_wp with epsilon(1.0_wp) in three functions Update zero detection logic from < to <= comparison Affects format_tick_value, format_tick_value_smart, and format_log_tick_value +3/-3

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[qodo-merge-pro]

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[qodo-merge-pro]

PR Code Suggestions ✨

Explore these optional code suggestions:

Category	Suggestion	Impact
Possible issue	Use a more appropriate zero-check tolerance Revert the zero-check tolerance from epsilon(1.0_wp) to a more practical value like the original 1.0e-10_wp. Using machine epsilon as an absolute tolerance is inappropriate and can result in incorrect formatting for values that are effectively zero. src/utilities/ticks/fortplot_tick_formatting.f90 [29] -if (abs_value <= epsilon(1.0_wp)) then +if (abs_value < 1.0e-10_wp) then Apply / Chat Suggestion importance[1-10]: 9 __ Why: The suggestion correctly identifies a significant logical flaw in using epsilon as an absolute tolerance for zero, which could lead to incorrect plot tick formatting and is a functional regression.	High
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