go-hass-agent: add macOS support

[mdevils]

Background

go-hass-agent was Linux-only until recently. Over a series of PRs merged into joshuar/go-hass-agent (#958, #960, #963, #964), it gained real macOS support: device/context setup, disk usage sensors, NVMe SMART status, and hardware temperature sensors, all implemented natively for macOS (no Linux emulation/compatibility layer). v14.17.0 -- the version this formula already installs -- is the first tagged release that includes all of that work, so go-hass-agent can now genuinely run on macOS, not just Linux.

This PR updates the formula to reflect that: it removes the depends_on :linux restriction and makes CGO_ENABLED conditional, since the agent's NVMe SMART support on macOS calls into IOKit/CoreFoundation via cgo (Linux has no such requirement and keeps building with CGO_ENABLED=0 as before).

What changed

• Removed depends_on :linux.
• ENV["CGO_ENABLED"] = OS.mac? ? "1" : "0" instead of a hardcoded "0".
• bottle do ... end, service do ... end, and test do ... end are all unchanged -- none of them needed platform-specific changes.

Verification

I confirmed the actual risk in this change -- whether v14.17.0's source really builds and runs correctly on macOS -- directly, on an M-series Mac:

• CGO_ENABLED=1 go build of the v14.17.0 tag succeeds cleanly.
• CGO_ENABLED=0 (the current hardcoded value) fails with undefined: NVMeDevice / undefined: OpenNVMe from the agent's NVMe SMART dependency -- confirming the existing hardcoded 0 would not have worked for macOS, and that the conditional is actually necessary, not just defensive.
• Ran the resulting binary the same way the formula's own test do block does (spawn with --server-port/--server-hostname, curl /register) and got a 200 response containing "Register".

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• I did not use AI/LLM to create this PR, or I disclosed the tool/model below and reviewed its output; I did not attribute commits to AI and will answer maintainer questions and review comments myself without AI/LLM.

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