[ENG-87] Implement price library

[xbtmatt]

Description

This PR introduces the standalone price representation module used for Dropset’s order and matching logic.

The implementation provides a deterministic, overflow-safe encoding of prices using a mantissa + biased exponent scheme without the usage of intermediate u128 values when storing price order info.

Summary of Changes

• Adds a standalone Rust module defining the canonical encoded price format
• Implements price_mantissa validation and bounds checking
• Adds biased exponent encoding with protection against underflow/overflow
• Adds conversion from (price_mantissa, base_scalar_exponent, quote_exponent) into the packed integer price.
• Ensures all intermediate arithmetic avoids u128 overflow using checked operations
• Implements decoding utilities for test/debug
• Unit tests:
  • Mantissa lower/upper boundary behavior
  • Precision limits
  • Exponent bias correctness
  • Encoding/decoding round-trip accuracy
• Mantissa bit-width, exponent bias, and masks follow the spec of 27-bit price mantissa and 5-bit exponent with a BIAS of 16
• Precision tests check extreme exponent differences
• Module is self-contained and ready for integration

[Copilot]

Pull request overview

This PR implements a new price library for encoding and decoding fixed-point decimal prices using a mantissa-exponent representation within a 32-bit integer. The library provides validation, encoding/decoding capabilities, and utilities for converting between different decimal representations.

Key Changes

• Introduces a price encoding scheme using 27 bits for mantissa and 5 bits for biased exponent
• Implements validated mantissa with strict digit bounds (8 significant digits)
• Provides macros for checked arithmetic operations and power-of-10 calculations with biased exponents

Reviewed changes

Copilot reviewed 8 out of 9 changed files in this pull request and generated 7 comments.

Show a summary per file

File	Description
price/src/lib.rs	Main library module defining constants, OrderInfo struct, and conversion logic with tests
price/src/validated_mantissa.rs	Wrapper type ensuring mantissa values are within valid 8-digit range
price/src/macros.rs	Utility macros for pow10 calculations and checked arithmetic operations
price/src/error.rs	Error enum for order information validation failures
price/src/encoded_price.rs	Encoding logic for packing mantissa and exponent into u32
price/src/decoded_price.rs	Decoding logic for extracting mantissa and exponent from u32
price/Cargo.toml	Package manifest with dependencies
Cargo.toml	Workspace update to include price crate
Cargo.lock	Lock file update for new price package

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[Copilot]

Pull request overview

Copilot reviewed 8 out of 9 changed files in this pull request and generated 17 comments.

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[Copilot]

Pull request overview

Copilot reviewed 8 out of 9 changed files in this pull request and generated 5 comments.

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[Copilot]

Pull request overview

Copilot reviewed 8 out of 9 changed files in this pull request and generated 11 comments.

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[xbtmatt]

Second round of addressing review comments and changes

[Copilot]

Pull request overview

Copilot reviewed 8 out of 12 changed files in this pull request and generated no new comments.

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[xbtmatt]

Third round of addressing review comments and fixes!

[Copilot]

Pull request overview

Copilot reviewed 8 out of 12 changed files in this pull request and generated 1 comment.

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[xbtmatt]

Fourth round of addressing review comments