Merge patch series "liveupdate: Remove limits on sessions and files"

Pasha Tatashin <pasha.tatashin@soleen.com> says:

Remove the fixed limits on the number of files that can be preserved
within a single session, and the total number of sessions managed by the
Live Update Orchestrator (LUO).

The core of the change is a transition from single contiguous memory
blocks for metadata serialization to a chain of linked blocks. This
allows LUO to scale dynamically.

1.  ABI Evolution:
- Introduced linked-block headers for both file and session
  serialization.
- Bumped session ABI version to v4.

2.  Memory Management & Security:
- Implemented a dynamic block allocation and reuse strategy. Blocks
  are allocated only when existing ones are exhausted and are reused
  during session/file removal cycles.
- Introduced KHO_MAX_BLOCKS (10000) as a safeguard against stupid
  excessive allocations or corrupted cyclic lists during restore.

3.  Expanded Selftests:
- Added new kexec-based tests verifying preservation of
  2000 sessions and 500 files per session.
- Added self-tests for many sessions and many files management.

* patches from https://patch.msgid.link/20260603154402.468928-1-pasha.tatashin@soleen.com:
liveupdate: change file_set->count type to u64 for type safety
liveupdate: avoid mixing cleanup guards with goto in luo_session_retrieve_fd
liveupdate: centralize state management into struct luo_ser
liveupdate: register luo_ser as KHO subtree
liveupdate: Extract luo_file_deserialize_one helper
liveupdate: Extract luo_session_deserialize_one helper
kho: add support for linked-block serialization
liveupdate: defer session block allocation and physical address setting
liveupdate: Remove limit on the number of sessions
liveupdate: Remove limit on the number of files per session
selftests/liveupdate: Test session and file limit removal
selftests/liveupdate: Add stress-sessions kexec test
selftests/liveupdate: Add stress-files kexec test

Link: https://patch.msgid.link/20260603154402.468928-1-pasha.tatashin@soleen.com
Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>