Inconsistency in the way promotion to `long double` is handled between x86_64 and other architectures, e.g. aarch64

## Description

I want to propose disabling promotion to from `double` to `long double` by default in Boost's math functions due to performance implications and architectural differences between platforms. Users who need higher precision can enable promotion with a policy.

Boost documentation on type promotion: https://live.boost.org/doc/libs/1_44_0/libs/math/doc/sf_and_dist/html/math_toolkit/policy/pol_ref/internal_promotion.html

### Current Behavior

- On x86_64: Promotes to 80-bit extended precision `long double` (15-bit exponent, 63-bit precision)
- On aarch64: Promotes to 128-bit quadruple precision `long double` (15-bit exponent, 112-bit precision). The ARMv8 ISA does not define a floating point type wider than 64 bits and so GCC uses a soft float implementation for the quadruple precision, 128-bit float.

### Issues with Current Behavior

1. Performance Impact
- Significant performance overhead from promotion to `long double`
- Larger performance delta between architectures (e.g., x86_64 vs aarch64) compared to standard library implementations

2. Architectural Inconsistency
- Different precision levels between platforms (63 bits vs 112 bits)
- Potentially unexpected behavior when moving code between architectures

3. Limited Benefit
- Numerical differences at these precision levels are typically negligible for most use cases
- Most applications that truly need extended precision would explicitly specify it