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>

src/llama-model-loader.h

@@ -126,8 +126,7 @@ struct llama_model_loader {
         const std::string & fname,
         std::vector<std::string> & splits, // optional, only need if the split does not follow naming scheme
         FILE * file,
-        bool use_mmap,
-        bool use_direct_io,
+        llama_load_mode load_mode,
         bool check_tensors,
         bool no_alloc,
         const llama_model_kv_override * param_overrides_p,