Big changes are still happening

oh boy this is taking way too long

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Rewritten kprint

kprint, the kernel print macro has been fully rewritten. The public macros have not changed, but internally, the macros now:

• Construct a kernel writer
• Call core::fmt::write on the kernel writer

The kernel writer collects the text of all calls made to it using core::fmt::write in an internal buffer, and on drop, it pushes a new entry into the kernel log ringbuffer in a format that is (currently only partially) syslog-compatible. Then, the kernel writer dispatches a log header and the full log text to all active log recievers (like UART or the basic framebuffer).

New Types

• PackedU8: A type which wraps all the bitwise logic for packing multiple pieces of data which are less than one byte into a byte
• UncheckedCell: A datatype with interior mutability, which can be uninitialized via MaybeUninit. When the cargo feature debug-checks is enabled, this type also checks for double initialization and uninitialized access
• NicheCell: A datatype with interior mutability, which can be uninitialized via Option. This datatype is designed to be used with values that can take advantage of niche optimization (where the datatype T has a value which is guaranteed to be invalid, like a NonZeroU64 being zero)

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and oh boy, the big refactor: redid kernel source tree, ... commit is gonna be one hell of a mess…