fix: force train split for json,csv,txt for test_datasets and misc doc changes (#3226)

* fix: force train split for json,csv,txt for test_datasets

* feat(doc): add info on mixing datasets for VLM

* feat(doc): max memory

* fix(doc): clarify lr groups

* fix: add info on vision not being dropped

* feat: add qwen3-vl to multimodal docs

* fix: add moe blocks to arch list

* feat(doc): improve mistral docs

* chore: add helpful link [skip-e2e]

* fix: add vram usage for mistral small

* Update link in docs/faq.qmd

Co-authored-by: salman <salman.mohammadi@outlook.com>

---------

Co-authored-by: Wing Lian <wing@axolotl.ai>
Co-authored-by: salman <salman.mohammadi@outlook.com>

docs/lr_groups.qmd

@@ -27,3 +27,9 @@ learning_rate: 2e-5
 In this example, we have a default learning rate of 2e-5 across the entire model, but we have a separate learning rate
 of 1e-6 for all the self attention `o_proj` modules across all layers, and a learning are of 1e-5 to the 3rd layer's
 self attention `q_proj` module.
+
+::: {.callout-note}
+
+We currently only support varying `lr` for now. If you're interested in adding support for others (`weight_decay`), we welcome PRs. See https://github.com/axolotl-ai-cloud/axolotl/blob/613bcf90e58f3ab81d3827e7fc572319908db9fb/src/axolotl/core/trainers/mixins/optimizer.py#L17
+
+:::