contracts-bedrock: cleanup libraries (#8907)

* contracts-bedrock: cleanup libraries

Updates the pragma in libraries to be more permissive, making it less
complex to import the libraries into different codebases. The actual
implementations enforce a particular version, so it is safe to allow
the libs to have permissive versioning contrainsts. Also update the
code to use the absolute path for imports relative from the project
root. Using this import pattern is the standard for the codebase.

* contracts-bedrock: remove warning

packages/contracts-bedrock/src/libraries/Arithmetic.sol

 // SPDX-License-Identifier: MIT
-pragma solidity 0.8.15;
+pragma solidity ^0.8.0;
 
 import { SignedMath } from "@openzeppelin/contracts/utils/math/SignedMath.sol";
 import { FixedPointMathLib } from "@rari-capital/solmate/src/utils/FixedPointMathLib.sol";

packages/contracts-bedrock/src/libraries/Constants.sol

 // SPDX-License-Identifier: MIT
 pragma solidity ^0.8.0;
 
-import { ResourceMetering } from "../L1/ResourceMetering.sol";
+import { ResourceMetering } from "src/L1/ResourceMetering.sol";
 
 /// @title Constants
 /// @notice Constants is a library for storing constants. Simple! Don't put everything in here, just

packages/contracts-bedrock/src/libraries/DisputeErrors.sol

 // SPDX-License-Identifier: MIT
 pragma solidity ^0.8.15;
 
-import "./DisputeTypes.sol";
+import "src/libraries/DisputeTypes.sol";
 
 ////////////////////////////////////////////////////////////////
 //                `DisputeGameFactory` Errors                 //

packages/contracts-bedrock/src/libraries/Encoding.sol

 // SPDX-License-Identifier: MIT
 pragma solidity ^0.8.0;
 
-import { Types } from "./Types.sol";
-import { Hashing } from "./Hashing.sol";
-import { RLPWriter } from "./rlp/RLPWriter.sol";
+import { Types } from "src/libraries/Types.sol";
+import { Hashing } from "src/libraries/Hashing.sol";
+import { RLPWriter } from "src/libraries/rlp/RLPWriter.sol";
 
 /// @title Encoding
 /// @notice Encoding handles Optimism's various different encoding schemes.

packages/contracts-bedrock/src/libraries/Hashing.sol

 // SPDX-License-Identifier: MIT
 pragma solidity ^0.8.0;
 
-import { Types } from "./Types.sol";
-import { Encoding } from "./Encoding.sol";
+import { Types } from "src/libraries/Types.sol";
+import { Encoding } from "src/libraries/Encoding.sol";
 
 /// @title Hashing
 /// @notice Hashing handles Optimism's various different hashing schemes.