Fix Mach port leak in alt_clock_gettime for macOS

[qingweizhang054]

Title: Fix Mach port leak in alt_clock_gettime for macOS

Description:
While reviewing the clock implementation for macOS (legacy versions < 10.12), I noticed a Mach port leak in alt_clock_gettime.

According to Mach kernel documentation, mach_host_self() returns a send right to the host's port which increments the port's reference count. This right must be released using mach_port_deallocate to prevent resource exhaustion in long-running processes.

Changes:

• Store the result of mach_host_self() in a local variable.
• Call mach_port_deallocate for the host port after obtaining the clock service.

Impact:

• Fixes a slow resource leak on macOS legacy systems.
• No impact on modern macOS (10.12+) as they use the native clock_gettime.