Encode session ids using protobufs.

[fancycode]

This will reduce their size and improve encoding / decoding performance.

Also fixes GO-2024-3106 (Stack exhaustion in Decoder.Decode in encoding/gob).

[coveralls]

Pull Request Test Coverage Report for Build 11555347272

Details

• 80 of 95 (84.21%) changed or added relevant lines in 4 files are covered.
• 10 unchanged lines in 4 files lost coverage.
• Overall coverage increased (+0.1%) to 59.22%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
proxy/proxy_server.go	3	4	75.0%
hub.go	28	30	93.33%
client/main.go	0	6	0.0%
sessionid_codec.go	49	55	89.09%

Files with Coverage Reduction	New Missed Lines	%
client/main.go	1	0.0%
mcu_proxy.go	2	60.78%
grpc_client.go	3	78.68%
dns_monitor.go	4	94.12%

Totals
Change from base Build 11552635147:	0.1%
Covered Lines:	10768
Relevant Lines:	18183

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💛 - Coveralls