More memory-efficient swan_path

[nluka]

Context

Swan has containers ("components") which store path data. A replacement for the swan_path data type is needed which is more memory efficient, and offers good runtime performance characteristics.

The current swan_path implementation is struct swan_path : std::array<char, ((MAX_PATH - 1) * 4) + 1>, an array of characters which holds up to the theoretical maximum length in bytes of a UTF-8 path which meets the MAX_PATH constraint in Windows.

The issue with this implementation is it always occupies 1037 bytes of memory, but very rarely uses all of it. Most paths are much shorter than MAX_PATH, the common case being <= 50 codepoints. To put this into perspective, if the average path is 50 ASCII characters + 1 NUL, then the swan_path data type wastes about 9.4MB per 10,000 objects. This is significant for components which store many elements, each containing one or sometimes multiple swan_path.

The main goal is to rework the swan_path implementation for the listed components and eliminate this memory wastage without hurting performance in key areas.

Constraints

Each component has some constraints imposed based on how the data in the containers is used:

• ImGuiListClipper constraint: requires container elements to be same size, no dynamic element sizes allowed. This is because list clipper demands that the container support random access, as iteration of the container does not always begin at the first element.

Constraints specific to a component are detailed in the dedicated section further down.

In general, the replacement of the underlying type for swan_path must:

• Provide member function char *data() noexcept
• Provide the ability to query its length in O(1) time, not O(n)

Components

Component	Current container type	ImGuiListClipper constraint?
explorer_window::cwd_entries	std::vector	Y
g_file_op_cmd_buf	std::vector	Y
g_pins	std::vector	Y
g_recent_files	circular_buffer	Y
g_completed_file_ops	circular_buffer	Y
explorer_window::wd_history	circular_buffer	N

explorer_window::cwd_entries

TODO

explorer_window::wd_history

TODO

g_file_op_cmd_buf

TODO

g_pins

TODO

g_recent_files

TODO

g_completed_file_ops

TODO