feat: add tanh (hyperbolic tangent) library

[coffeexcoin]

PR-Codex overview

This PR introduces a new library, LibTanh, for calculating the hyperbolic tangent of a number in Solidity, along with a set of tests in LibTanhTest to verify its functionality and handle overflow cases.

Detailed summary

• Added LibTanh library with functions tanh and rawTanh.
• Implemented private function _tanh for internal calculations.
• Introduced error handling for overflow with TanhOverflow.
• Created LibTanhTest contract with multiple test cases for tanh.
• Added tests for overflow scenarios and expected results for various inputs.

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PR Summary

Medium Risk
Introduces new fixed-point math based on expWad with explicit overflow behavior; mistakes here could affect any downstream financial calculations that rely on tanh outputs.

Overview
Adds LibTanh, a WAD-scaled hyperbolic tangent implementation using FixedPointMathLib.expWad, with two entrypoints: tanh (reverts with TanhOverflow) and rawTanh (saturates to 1e18 on overflow).

Adds LibTanh.t.sol test coverage for expected outputs across several inputs and verifies both revert-on-overflow and saturation behavior.

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Debug import left in production library code

Low Severity

The console2 import from forge-std is a debugging/testing utility that was left in the production library code. It's imported but never actually used in the library. The forge-std package is a testing framework dependency and this import doesn't belong in production smart contract code.