fix(sdk): store assistant tool calls under the tool_calls message key

[alemorale7777]

Problem

RequestBuilder::add_message_with_tool_call (in the mistralrs SDK crate) attaches the assistant's tool calls to the message under the key "function":

self.messages.push(IndexMap::from([
    ("role".to_string(), Either::Left(role.to_string())),
    ("content".to_string(), Either::Left(text.to_string())),
    ("function".to_string(), Either::Right(tool_messages)),
]));

Every consumer of an assistant tool-call message reads the standard OpenAI/HF key "tool_calls", not "function":

• chat_template.rs renders tool calls from message.get_mut("tool_calls") and clears content based on contains_key("tool_calls").
• The agentic engine matches on "tool_calls" (agentic_session.rs, agentic_loop.rs).
• The server path builds the identical structure under "tool_calls" (chat_completion.rs).

Because nothing reads a message-level "function" key, the tool call is silently dropped: the chat template renders the assistant turn without its tool call, and the following tool result then has no preceding call, breaking multi-round tool use.

This is the SDK's recommended API for tool-call messages, and it is used by the SDK's own Agent loop (agent.rs, both the streaming and non-streaming paths) and by the examples/advanced/tools example, so SDK-driven tool conversations are affected.

Fix

Use the "tool_calls" key. The value structure is already correct (each entry has id, type, and a nested function object with name/arguments) and matches what the server path emits, so this is a one-character-key change with no other behavior difference. Added a unit test asserting the emitted message uses tool_calls (not function) and preserves the nested call structure.

[github-actions]

Code Metrics Report

━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
 Language              Files        Lines         Code     Comments       Blanks
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
 C Header                 23         4454         3116          790          548
 CSS                       3          282          252            6           24
 CUDA                    119        23681        19217         1704         2760
 Dockerfile                1           35           19            9            7
 HTML                      2           27           27            0            0
 JavaScript                3          577          562           12            3
 Jinja2                    7          694          656            5           33
 JSON                     27        15864        15861            0            3
 Makefile                  1           18           16            0            2
 MDX                      36         5901            0         4327         1574
 Metal Shading Lan|       37        14287        11284         1136         1867
 PowerShell                1          656          570           31           55
 Python                  151        12284        10191          484         1609
 Shell                     3         1062          843          117          102
 Plain Text               53        10687            0         9209         1478
 TOML                     28         1368         1189           39          140
 TypeScript               11         1641         1404           66          171
 YAML                      3           25           23            2            0
─────────────────────────────────────────────────────────────────────────────────
 Jupyter Notebooks         3          122           83           23           16
 |- Markdown               1           60           30           22            8
 |- Python                 1          122          113            1            8
 (Total)                              304          226           46           32
─────────────────────────────────────────────────────────────────────────────────
 Markdown                273        11726            0         8736         2990
 |- BASH                  23          295          217           46           32
 |- Dockerfile             2            5            5            0            0
 |- JSON                   6          289          289            0            0
 |- PowerShell             1            1            1            0            0
 |- Python               135         7239         6021          310          908
 |- Rust                  62         3820         2838          388          594
 |- TOML                   7           77           65            0           12
 (Total)                            23452         9436         9480         4536
─────────────────────────────────────────────────────────────────────────────────
 Rust                    674       299702       267081         5872        26749
 |- Markdown             413         9761          452         8126         1183
 (Total)                           309463       267533        13998        27932
─────────────────────────────────────────────────────────────────────────────────
 Svelte                   19         1969         1826           51           92
 |- CSS                    1            4            4            0            0
 |- JavaScript            19          921          767           25          129
 (Total)                             2894         2597           76          221
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
 Total                  1478       429656       345022        41537        43097
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━