feat: add show CLI tool to parse and display quotes

[hyperfinitism]

What's changed

• Add tools/show/show.go: a CLI tool show that reads a TDX quote (in binary, proto, or textproto format), parses it into a tdx.QuoteV4 protobuf, and writes it out in the requested format (currently only textproto is supported).
  • Parsing logic is imported from tools/check/check.go
  • Writing logic is imported from tools/attest/attest.go
• Add tools/show/README.md: documents the tool's purpose, flags, defaults, and usage, matching the style of other CLI tools in the repo.

Test

Environment

• VM: Google Compute Engine C3
• OS: Ubuntu 24.04
• Kernel: 6.14.0-1017-gcp
• Go: 1.22.2

bin→textproto

sudo ./attest -in deadbeef -inform hex -out quote.bin -outform bin
./show -in quote.bin -inform bin -outform textproto -out quote-bin-to-textproto.txt
cat ./quote-bin-to-textproto.txt

textproto→textproto

sudo ./attest -in deadbeef -inform hex -out quote.txt -outform textproto
./show -in quote.txt -inform textproto -outform textproto -out quote-textproto-to-textproto.txt
cat ./quote-textproto-to-textproto.txt

bin→textproto (stdout)

sudo ./attest -in deadbeef -inform hex -out quote.bin -outform bin
./show -in quote.bin -inform bin -outform textproto

Each script results:

header:  {
  version:  4
  attestation_key_type:  2
  tee_type:  129
  qe_svn:  "\x00\x00"
  pce_svn:  "\x00\x00"
  qe_vendor_id:  "\x93\x9ar3\xf7\x9cL\xa9\x94\n\r\xb3\x95\x7f\x06\x07"
  user_data:  "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00"
}
td_quote_body:  {
  ...

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