refactor: bisect all accumulating savings calculations

[alex-rie]

🔗 Linked issue

❓ Type of change

• 📖 Documentation (updates to the documentation, readme or JSDoc annotations)
• 🐞 Bug fix (a non-breaking change that fixes an issue)
• 👌 Enhancement (improving an existing functionality like performance)
• ✨ New feature (a non-breaking change that adds functionality)
• 🧹 Chore (updates to the build process or auxiliary tools and libraries)
• ⚠️ Breaking change (fix or feature that would cause existing functionality to change)

📚 Description

📝 Checklist

• I have linked an issue or discussion.
• I have updated the documentation accordingly.

[Copilot]

Pull Request Overview

This PR refactors the accumulating savings calculations to use a unified bisection approach instead of specialized closed-form financial functions. The change removes three accumulating-taxed variants (pmtAccumulatingTaxed, pvAccumulatingTaxed, and nperAccumulatingTaxed) from the financial utilities and replaces their usage with calls to bisectByEndValue across the savings calculators.

Key changes:

• Removed three accumulating-taxed financial functions that handled capital gains tax calculations
• Updated savings calculators (payment, start value, duration) to use bisection method for accumulating distribution calculations
• Simplified test expectations by removing special-case tolerance handling for monthly intervals

Reviewed Changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
src/utils/financial.ts	Removed pmtAccumulatingTaxed, pvAccumulatingTaxed, and nperAccumulatingTaxed functions
src/calculators/savings-payment.ts	Replaced pmtAccumulatingTaxed with bisectByEndValue for accumulating distribution
src/calculators/savings-start-value.ts	Replaced pvAccumulatingTaxed with bisectByEndValue for accumulating distribution
src/calculators/savings-duration.ts	Replaced nperAccumulatingTaxed with bisectByEndValue for accumulating distribution
test/utils/savings-utils.test.ts	Removed special-case tolerance handling for monthly save/interest intervals

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[Copilot]

Pull Request Overview

Copilot reviewed 5 out of 5 changed files in this pull request and generated 1 comment.

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