Fix date and time bugs in EXT4

[dkovba]

• Fixes EXT4 timestamp encoding for pre-1970 dates
• Fixes EXT4 timestamp decoding for pre-1970 dates
• Fixes the creation date
• Fixes a UInt32 overflow

Resolves the following failures in the added tests:

Swift/arm64e-apple-macos.swiftinterface:38198: Fatal error: Double value cannot be converted to UInt64 because the result would be less than UInt64.min
error: Process '/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/libexec/swift/pm/swiftpm-testing-helper --test-bundle-path /Users/Dmitry/Apple/containerization/.build/arm64-apple-macosx/debug/containerizationPackageTests.xctest/Contents/MacOS/containerizationPackageTests --filter encodeNegativeTimestamp /Users/Dmitry/Apple/containerization/.build/arm64-apple-macosx/debug/containerizationPackageTests.xctest/Contents/MacOS/containerizationPackageTests --testing-library swift-testing' exited with unexpected signal code 5

✘ Test decodeNegativeTimestamp() recorded an issue at TestEXT4Format+Create.swift:100:6: Caught error: not a valid EXT4 superblock
✘ Test decodeNegativeTimestamp() failed after 0.003 seconds with 1 issue.
✘ Suite NegativeTimestampRoundtripTests failed after 0.004 seconds with 1 issue.
✘ Test run with 1 test in 1 suite failed after 0.004 seconds with 1 issue.