Add MCP_TOOL_TIMEOUT_MSEC default value only for tool calls.

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I've submitted a PR for updating the request timeout, and reviewed it a bit, so we can set the default request timeout for all requests. Now, I'd like to pull out the function for retrieving the ENV into a helper function and reuse it for only client tool calls.

Here's the PR I want to build on:

https://github.com/modelcontextprotocol/typescript-sdk/pull/1854

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Add an env for default tool call milliseconds in client.ts.

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Only having it for all requests.

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Here is how I envision the precedence:

All requests have a 60-second default timeout. The timeout for a given request is resolved in the following order of precedence (highest first):
Per-request timeout option — passed directly in the request options.
MCP_TOOL_TIMEOUT_MSEC — environment variable that applies only to tools/call requests.
MCP_REQUEST_TIMEOUT_MSEC — environment variable that applies to all requests.
60,000 ms — hardcoded fallback.

By the way, I was also thinking about defaulting to MCP_TOOL_TIMEOUT - to align with claude, which uses typescript SDK? However, this seems less idiomatic because this code base seems to append MSEC.

Start in client.ts and review PR #1854 to understand the existing request-timeout environment lookup. Trace how tools/call requests resolve their timeout, then verify that the documented precedence is applied and that other request types retain the general timeout behavior.