feat(math): implement fast Yul bit-search indexer and unit tests (#751)

[Francis6-git]

Description

This PR implements a constant-time $O(1)$ bit-search library in Yul (contracts/math/YulBitSearch.sol) to locate the Most Significant Bit (MSB) and Least Significant Bit (LSB) in a uint256 word.

High-level Solidity while loops iterate bit-by-bit, causing substantial gas overhead on large numbers. This implementation uses an 8-stage binary search bitwise shift approach directly in Yul inline assembly, guaranteeing predictable constant gas execution regardless of the bit position.

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Changes Included

• contracts/math/YulBitSearch.sol: Implemented mostSignificantBit and leastSignificantBit using constant-time binary search shifts in Yul.
• test/math/YulBitSearch.test.ts: Added comprehensive Vitest suite covering singleton bits ($2^0$ to $2^{255}$), dense bit masks (MAX_UINT256), edge values, and zero-word handling.

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Test Results

Ran unit test suite via Vitest targeting the newly added test file:

npx vitest run test/math/YulBitSearch.test.ts

 RUN  v4.1.11 C:/Users/BUMBLECODE/Documents/Projects/GasGuard

 ✓ test/math/YulBitSearch.test.ts (3 tests) 40ms
   ✓ YulBitSearch (3)
     ✓ returns zero for a zero word 4ms
     ✓ finds every singleton bit position 31ms
     ✓ handles edge and dense values 1ms

 Test Files  1 passed (1)
      Tests  3 passed (3)
   Start at  16:51:17
   Duration  1.50s (transform 125ms, setup 0ms, import 203ms, tests 40ms, environment 0ms)

Closes #751

[mijinummi]

Hello @Francis6-git , thank you for your contribution.

Please kindly fix the ci failures.