Improve logging and lockdown features

[timflyio]

Adds improvements to make it easier to run a somewhat open tokenizer, including restrictions to limit general internet access (require fly src), and improved auditing to help track down abuse if it happens.

• Adds a lot more information to the log files, including the unwrapped/parsed/redacted token, source ip, and fly src, when possible.
• Adds an option to reject any request that does not carry fly-src. The intention here is for allowing a somewhat open fly proxy that cant be abused from outside fly.
• Adds a tool for generating a specific type of wrapped token, as used by my pilot proxy project.
• Adds a cmd line option for printing out the seal key so you dont have to grep it from logs.
• Stores the parsed fly-src in request context to avoid parsing it multiple times.
• Get rid of internal flysrc parsing library and use github.com/superfly/flysrc-go.

[timflyio]

tested deploy from timapp branch in xau, running command from another machine in xau:
curl -H "Proxy-Tokenizer: CUg3e/QsJ9F8joj8SGwtRLRO1+ov+lqv+6QaYBEoSlmK9NORKPnfjICXkLl8zMy2bW35sRZPmJixAj0Qu2yKOT+q32/JBnLuYv3US6MSdgTJmnSg+8S7w8c+SkJQR6h4RIAaO68cLqLsB6/jLcl1Bc6Pf7FObIx+29WN4cE15C+bKXDM3O8SA7A33CcLpDHRDJzGoukFM20TobN4A+ZsBfDoejVU53Iv4I8u/oBmKbRfhuT0T2igpAfVaxB/5gyeMMgGTY8vYI69TvjVU0006rp3lXWXF93G5AiYsSfMwPNChfWrGXmKwRd0hVYpDTvBRFebd0lPlVE=" -H "fly-src-optin: *" -x https://tokenizer.fly.dev:8443 http://timflyio-go-example.fly.dev