vmmap: Fix vmmap according to failing unit tests

[rennergade]

#465 adds unit tests to VMMap to test for correctness, a few of the added tests are failing, mostly related to changing protection. Its great that we have these now so lets fix these problems.

These are the results when running the tests:

failures:
    memory::vmmap::tests::test_change_prot_end_of_region
    memory::vmmap::tests::test_change_prot_exact_boundaries
    memory::vmmap::tests::test_change_prot_middle_of_region
    memory::vmmap::tests::test_change_prot_multiple_times
    memory::vmmap::tests::test_change_prot_spanning_multiple_regions
    memory::vmmap::tests::test_change_prot_to_none
    memory::vmmap::tests::test_change_prot_to_same_value
    memory::vmmap::tests::test_find_map_space_with_hint_alignment_in_pages

test result: FAILED. 14 passed; 8 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s

[ChinmayShringi]

change_prot (lines 563-603)
The function fails to properly split memory regions when changing protection flags, modifies entries in-place during iteration while also scheduling overlapping intervals for insertion, which creates extra fragments instead of clean splits. The logic doesn't correctly handle the three parts of a split: "before target", "inside target", "after target"

Current broken logic:

// Modifies ent_start locally (doesn't affect the actual interval)
ent_start = new_region_start_page;  // Local variable only

// Then still modifies the entire original entry
entry.prot = new_prot;  // Changes whole range

// Then inserts overlapping intervals
insert_overwrite(interval, ...);  // Creates fragments

Affects:

1. test_change_prot_end_of_region
2. test_change_prot_exact_boundaries
3. test_change_prot_middle_of_region
4. test_change_prot_multiple_times
5. test_change_prot_spanning_multiple_regions
6. test_change_prot_to_none
7. test_change_prot_to_same_value

find_map_space_with_hint (lines 945-968)
The alignment calculation doesn't ensure both boundaries are aligned, returns (aligned_end - rounded_size, aligned_end) The start boundary may not be aligned to pages_per_map,then calculate aligned start position directly

Affects:

1. test_find_map_space_with_hint_alignment_in_pages

[rennergade]

Awesome that makes sense. Try fixing that and see if the tests get fixed. If so PR it.

Thanks!