[integration][ollama] Tolerate tool schemas without a 'required' key

[Zhuoxi2000]

Linked issue: #1014

Purpose of change

OllamaChatModelConnection.convertToOllamaTools assumed the tool schema always carries a required list, but required is optional in JSON Schema and SchemaUtils.generateSchema only emits it when at least one parameter is required. A Java @Tool whose parameters are all optional therefore produced a valid schema that crashed the Ollama connector with an NPE before the request reached the server. The same shape can come from external tools (e.g. an MCP tool with only optional parameters), so this hardens the consumer rather than changing SchemaUtils: a missing required list is treated as empty, and all-optional tools convert normally with every property marked required(false).

Tests

New OllamaChatModelConnectionTest (the module previously had no connection test): a schema without a required key converts with every property optional, and a schema with a required key still marks the listed parameters required. Both are pure unit tests of the conversion — no Ollama server needed. convertToOllamaTools was narrowed from private to package-private for test access.

API

None.

Documentation

• doc-needed
• doc-not-needed
• doc-included

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If yes, include a Generated-by: <tool name and version> (<model name and version>) line, for example Generated-by: Claude Code 2.1.226 (Claude Opus 4.6), in the commit message so it reaches Git history. Repeat the same line here for reviewer visibility. See the ASF generative tooling guidance.

Generated-by: Claude Fable 5