Claude review: lib/fonts: Create font_data_t from struct console_font with font_data_import()

[Claude Code Review Bot <claude-review@example.com>]

Patch Review

Centralizes the font import logic from fbcon and newport_con.

**Issue 1**: The `int size` and `int alloc_size` variables are signed but used for sizes. While the `check_mul_overflow` / `check_add_overflow` macros handle this correctly (they detect overflow for the destination type), using `unsigned int` would be more idiomatic for size values. This matches the pattern from the original fbcon code though.

**Issue 2**: The source-side memcpy index is not overflow-checked:
```c
for (i = 0; i < charcount; ++i)
    memcpy(font_data->data + i * h * pitch, data + i * vpitch * pitch, h * pitch);
```
`i * vpitch * pitch` on the source side could overflow if `vpitch` is large. `vpitch` comes from user space (the VT ioctl). While the existing code had the same pattern, this is the "proper" refactored version — adding `check_mul_overflow` for `vpitch * pitch` and `i * vpitch * pitch` would improve robustness. In practice, vpitch is typically 32 and pitch is at most 4, so the maximum is `512 * 32 * 4 = 65536`, well within range.

**Issue 3**: The doc comment says `@calc_sum` but the parameter is `calc_csum`, and "chechsum" should be "checksum".

The newport_con simplification removing the `vpitch != 32` check is a good improvement — newport_con previously rejected fonts where vpitch != 32, but font_data_import handles any vpitch correctly.

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