docs: Add comprehensive NatSpec documentation to core libraries and types

[Dark-Brain07]

Related Issue

N/A (Improves documentation quality and coverage across core libraries)

Description of changes

This PR enhances the codebase documentation by adding comprehensive NatSpec comments to 14 core library and type files. It specifically focuses on clarifying low-level implementation details, bit manipulation logic, and assembly operations in the libraries and types directories.

Detailed changes:

• Added robust library-level documentation explaining the purpose, usage, and memory layout (where applicable) for each file.
• Documented over 50+ functions with @notice, @dev, @param, and @return tags.
• Enhanced developer comments for assembly blocks and bitwise operations to improve readability and maintainability.
• Added EIP-1153 transient storage explanations to CurrencyReserves.sol.
• Clarified memory layout for packed structs in Slot0.sol and PoolKey.sol.
• Documented Currency value type and associated library functions.

Files improved:

• src/libraries/: BitMath.sol, CurrencyReserves.sol, FixedPoint96.sol, FixedPoint128.sol, LiquidityMath.sol, Lock.sol, ParseBytes.sol, SafeCast.sol, UnsafeMath.sol, NonzeroDeltaCount.sol, CurrencyDelta.sol
• src/types/: BalanceDelta.sol, BeforeSwapDelta.sol, PoolId.sol, Currency.sol, Slot0.sol, PoolOperation.sol
• test/: Added FixedPointLibraries.t.sol for coverage.