fix(tools): respect function.strict = false in to_new_openai

[bahaaza]

Description

When a tool schema sets strict = false on the ["function"] key (e.g. mcphub's use_mcp_tool), to_new_openai ignored it because it only checked parameters.strict. This caused enforce_strictness to be applied even when the tool explicitly opted out.

For tools with dynamic schemas like tool_input (an object with no predefined properties but additionalProperties = false), forcing strict mode made the schema reject all properties — the LLM would send empty tool_input: {} or the API would reject the schema entirely, resulting in silent tool failure.

Root Cause

-- Before: only checked parameters.strict (nil for mcphub tools)
if opts.strict_mode and not schema["function"].parameters.strict then
    schema = M.enforce_strictness(schema)
end

mcphub sets strict = false on schema["function"].strict, not on schema["function"].parameters.strict, so the opt-out was never seen.

Fix

Resolve the tool's strict preference by checking function.strict first, falling back to parameters.strict. Enforcement is skipped only when the resolved value is explicitly false:

local tool_strict = schema["function"].strict
if tool_strict == nil then
    tool_strict = schema["function"].parameters.strict
end
if opts.strict_mode and tool_strict ~= false then
    schema = M.enforce_strictness(schema)
end

function.strict	parameters.strict	strict_mode	Enforce?
nil	nil	true	✅ Yes
true	any	true	✅ Yes
false	any	true	❌ No
any	any	false	❌ No

AI Usage

CodeCompanion (Claude) was used to help trace the execution path and draft the fix. The core analysis, root cause identification, and fix logic were directed by me.

Related Issue(s)

Fixes silent tool failure when using mcphub.nvim with the OpenAI Responses adapter (strict_mode = true).

Screenshots

N/A — logic-only change, no UI impact.

Checklist

• I've read the contributing guidelines and have adhered to them in this PR
• I confirm that this PR has been majority created by me, and not AI (unless stated in the "AI Usage" section above)
• I've run make all to ensure docs are generated, tests pass and StyLua has formatted the code
• (optional) I've added test coverage for this fix/feature
• (optional) I've updated the README and/or relevant docs pages