Adds more tests for the math and arithmetic packages to increase overall test coverage.

- Adds tests for Pow, Exp, Exp2, Log, Log2, Log10, Sin, Cos, Tan, Floor, Ceil, Round, Trunc, Mod, and Hypot in math_extra_test.go.

- Adds tests for AddWithMode, MulWithMode, DivWithMode, Equal, Less, Min, Max, and slice operations in arithmetic_extra_test.go.

- Corrects precision issues in math_extra_test.go.

Adds more tests for the convert package to increase overall test coverage.

- Adds tests for FromFloat64 and ToFloat64 in convert_extra_test.go.

Adds more tests for the types package to increase overall test coverage.

- Adds tests for Error, String, GoString, Class, and leadingZeros10 in types_extra_test.go.

Adds more tests for the arithmetic package to increase overall test coverage.

- Adds tests for AddWithMode, MulWithMode, and DivWithMode in arithmetic_extra_test.go.

Adds more tests for the arithmetic package to increase overall test coverage.

- Adds tests for MulWithMode and DivWithMode in arithmetic_extra_test.go.

Adds more tests for the convert package to increase overall test coverage.

- Adds tests for FromFloat64WithMode in convert_extra_test.go.

Adds more tests for the convert package to increase overall test coverage.

- Adds tests for FromFloat64WithMode in convert_extra_test.go.

- Apply general refactoring and cleanup to core float16 files.

…licates in ToFloat16/ToSlice16

…ounding

… across rounding modes

…add Bits/FromBits; implement CopySign

…omplete)

- Add .golangci.yml with standard Go linters
- Enable gofmt, govet, staticcheck, misspell, etc.
- Set timeout and complexity thresholds

Add BFloat16 Add/Sub/Mul/Div with IEEE and strict modes, overflow/underflow
detection, and configurable rounding. Fix golangci-lint v2 config. Remove
temporary calc file.