[release-1.0] Cherry-pick #3574: Update the gVisor release to 20261102.0 - #3576

gvisor-default gains v7, release 20261102.0, as its default version. v6 stays enabled, so actors with memory snapshots taken on v6 still restore with their memory.

The new gVisor release includes some reliability fixes such as:

• Systrap no longer crashes sandboxes at high density. It now recognizes host stalls, such as a cgroup freeze, and stops killing stub threads that only look stuck (google/gvisor@a5b7936e84dd).
• Resumed actors no longer fire all their pending timers at once, because CLOCK_MONOTONIC stops counting checkpointed time. Clock reads are fast right after a restore (google/gvisor@25172e526f45).
• Apps no longer freeze while a large memory region loads during a background restore, which lowers resume latency for big actors (google/gvisor@ffc048011e1b, google/gvisor@ae286a28ef26).
• Checkpoint no longer stats every cached file. For actors with many files, such as node_modules, the pause drops from seconds to milliseconds (google/gvisor@8229bcb7a7b6).
• Disk-backed overlay pages no longer count as memory after a restore, and long-lived sandboxes no longer grow memory for each file they touch (google/gvisor@aa767e4c43d0, google/gvisor@b24cc9724102).

AI use: AI-assisted, I reviewed and tested it.

• Tests pass
• Docs updated