Update Rust crate bigdecimal to v0.4.9

[renovate]

This PR contains the following updates:

Package	Type	Update	Change
bigdecimal	dependencies	patch	=0.4.8 -> =0.4.9

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Release Notes

akubera/bigdecimal-rs (bigdecimal)

v0.4.9

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Changes

• Add methods BigDecimal::{powi, powi_with_context} for raising a decimal to a i64 power

  • the powi uses Default Context

• Add methods BigDecimal::mul_with_context for efficient multiplication to fixed precision

  • uses precision and rounding-mode in the Context

• Add method BigDecimal::decimal_digit_count, returning number of decimal digits (i.e. precision) of the number

• Add method BigDecimal::order_of_magnitude, returning position of most significant digit of this decimal

• Add method BigDecimal::is_one_quickcheck, returning Option<bool> indicating if the value is 1.0 if it can be calculated without allocating, or None if too large

  • Replaced is_one in multiplication methods when used for optimizations
    • Should test if that actually speeds it up
  • Eg value 1.00000000000000000000000000000000000000000 is stored internally as
    [4870020673419870208, 16114848830623546549, 293] E -41 and it's hard to tell this is equivalent to 1

• Add optimizations to inverse

  • small powers of ten will simply flip their scale 1/10e-5 -> 10e5
  • convert to f64 to make initial guess when before iterative algorithm

• Add Context::invert(&self, BigDecimalRef), equivalent to BigDecimal::inverse_with_context(&self, &ctx)

  • Still has a bug where rounding ignores sign, affecting floor/ceiling modes

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