args: refactor mlock/mmap/directio into load-mode (#20834)

* args: overhaul mmap/mlock/dio into single arg

Signed-off-by: Aaron Teo <aaron.teo1@ibm.com>

* docs: update docs with llama-gen-docs

Signed-off-by: Aaron Teo <aaron.teo1@ibm.com>

* chore: satisfy code quality

Signed-off-by: Aaron Teo <aaron.teo1@ibm.com>

* args: make the `+` sign an actual modifier now

Signed-off-by: Aaron Teo <aaron.teo1@ibm.com>

* chore: general code clean up + comments

Signed-off-by: Aaron Teo <aaron.teo1@ibm.com>

* arg: fix deprecated flags support

Signed-off-by: Aaron Teo <aaron.teo1@ibm.com>

* arg: quick sanity check

Signed-off-by: Aaron Teo <aaron.teo1@ibm.com>

* bench: sync llama-bench argument parsing

Signed-off-by: Aaron Teo <aaron.teo1@ibm.com>

* fix: bugfix variable behaviour + llama-bench lm column size

Signed-off-by: Aaron Teo <aaron.teo1@ibm.com>

* arg: inverse commands should do the opposite instead of doing nothing

Signed-off-by: Aaron Teo <aaron.teo1@ibm.com>

* bench: fix incorrect dash

Signed-off-by: Aaron Teo <aaron.teo1@ibm.com>

* bench: fix missing modifiers for deprecated flags

Signed-off-by: Aaron Teo <aaron.teo1@ibm.com>

* llama: switch back to thread_local

Signed-off-by: Aaron Teo <aaron.teo1@ibm.com>

* arg: switch back to single enum

Signed-off-by: Aaron Teo <aaron.teo1@ibm.com>

* docs: update arg docs

Signed-off-by: Aaron Teo <aaron.teo1@ibm.com>

* chore: fix missing `mlock` from llama_load_mode_from_str + cleanup llama-bench

Signed-off-by: Aaron Teo <aaron.teo1@ibm.com>

* llama: fix mlock not activating

Signed-off-by: Aaron Teo <aaron.teo1@ibm.com>

* arg: add deprecation warning when old and new flags are combined

Signed-off-by: Aaron Teo <aaron.teo1@ibm.com>

* arg: cont add comment for todo in the future

Signed-off-by: Aaron Teo <aaron.teo1@ibm.com>

* docs: sync with upstream

Signed-off-by: Aaron Teo <aaron.teo1@ibm.com>

* docs: re-sync with upstream again

Signed-off-by: Aaron Teo <aaron.teo1@ibm.com>

---------

Signed-off-by: Aaron Teo <aaron.teo1@ibm.com>

tests/test-model-load-cancel.cpp

@@ -16,7 +16,7 @@ int main(int argc, char *argv[] ) {
 
     llama_backend_init();
     auto params = llama_model_params{};
-    params.use_mmap = false;
+    params.load_mode = LLAMA_LOAD_MODE_NONE;
     params.progress_callback = [](float progress, void * ctx){
         (void) ctx;
         return progress > 0.50;