Derive BastionID

[AlCutter]

This PR derives a new key to be used to authenticate the witness to a Bastion host.

I've done some refactoring to simplify/reuse code where possible to avoid mistakes in the future.

Key derivation results remain the same with the refactoring:

Before

----------------------------------------------------------- Trusted OS ----
Serial number ..............: 720A9DEAD4391E1E
Secure Boot ................: false
SRK hash ...................:
Revision ...................: a2c259b
Version ....................: 0.1.2-11-ga2c259b
Runtime ....................: go1.22.0 tamago/arm
Link .......................: false
MAC ........................: c6:08:a0:62:04:44
IdentityCounter ............: 0
Witness/Identity ...........: DEV:ArmoredWitness-misty-snow+4235d37b+ATQcX3zXpdLJdudAP97VhTkO4m0DEyld9ndttS/XdIKq
Witness/IP .................:
Witness/AttestationKey .....: DEV:AW-ID-Attestation-720A9DEAD4391E1E+ca59d820+AZhTXIbOHFbhQrHf22YK+4lLMsCfBrzA3zdA3IP5PaZh

After

----------------------------------------------------------- Trusted OS ----
Serial number ..............: 720A9DEAD4391E1E
Secure Boot ................: false
SRK hash ...................:
Revision ...................: ee18b13
Version ....................: 0.1.2-17-gee18b13
Runtime ....................: go1.22.0 tamago/arm
Link .......................: false
MAC ........................: c6:08:a0:62:04:44
IdentityCounter ............: 0
Witness/Identity ...........: DEV:ArmoredWitness-misty-snow+4235d37b+ATQcX3zXpdLJdudAP97VhTkO4m0DEyld9ndttS/XdIKq
Witness/IP .................:
Witness/AttestationKey .....: DEV:AW-ID-Attestation-720A9DEAD4391E1E+ca59d820+AZhTXIbOHFbhQrHf22YK+4lLMsCfBrzA3zdA3IP5PaZh
Witness/AttestedIdentity ...: [below]

ArmoredWitness ID attestation v1
720A9DEAD4391E1E
0
DEV:ArmoredWitness-misty-snow+4235d37b+ATQcX3zXpdLJdudAP97VhTkO4m0DEyld9ndttS/XdIKq

— DEV:AW-ID-Attestation-720A9DEAD4391E1E ylnYIEjwPNzNhE6A6Mx/4zhes5Wxg+45gcCO9atyhu6bucDCrf/99BPSO4SQwdDxHAdPRod53cicvfgCXskTMMv/CgI=

Witness/AttestedBastionID ..: [below]

ArmoredWitness BastionID attestation v1
720A9DEAD4391E1E
0
3a8a5615f38f0e3388d389d031353a6041acd12b30b38d5b6ddcaf16fd01dcc1

— DEV:AW-ID-Attestation-720A9DEAD4391E1E ylnYIC9IFCP5AKb34hlD9PWAUogTA6cIV+7z5OMr7LNfLMZpKUnlclQ25wPl4ka7giIxOQ4WxcsfKw+eeImN5b3f9AQ=

----------------------------------------------------------- Trusted OS ----

Towards transparency-dev/armored-witness/issues/253

[AlCutter]

Worth reviewing commit-by-commit.

[AlCutter]

I've just rebased onto main with #310 merged.