[backport#17617] doc: unify unix epoch time descriptions
Summary:
d94d34f05f4ae3efa07de409489d68bbcc216346 doc: update developer notes wrt unix epoch time (Jon Atack)
e2f32cb5c5c7f2b1d1fc7003587b6573fb59526a qa: unify unix epoch time descriptions (Jon Atack)
Pull request description:
Closes #17613. Updated call sites: mocktime, getblockheader, getblock, pruneblockchain, getchaintxstats, getblocktemplate, setmocktime, getpeerinfo, setban, getnodeaddresses, getrawtransaction, importmulti, listtransactions, listsinceblock, gettransaction, getwalletinfo, getaddressinfo Commands for testing manually: ``` bitcoind -help-debug | grep -A1 mocktime bitcoin-cli help getblockheader bitcoin-cli help getblock bitcoin-cli help pruneblockchain bitcoin-cli help getchaintxstats bitcoin-cli help getblocktemplate bitcoin-cli help setmocktime bitcoin-cli help getpeerinfo bitcoin-cli help setban bitcoin-cli help getnodeaddresses bitcoin-cli help getrawtransaction bitcoin-cli help importmulti bitcoin-cli help listtransactions bitcoin-cli help listsinceblock bitcoin-cli help gettransaction bitcoin-cli help getwalletinfo bitcoin-cli help getaddressinfo ```
Backport of Core PR17617 and PR14981
Note: used the newly introduced constant in two instances not covered in the backport, specifically in getrawtransaction and getblocktemplate
Test Plan:
ninja all check check-functional
Reviewers: #bitcoin_abc, Fabien
Reviewed By: #bitcoin_abc, Fabien
Subscribers: Fabien
Differential Revision: https://reviews.bitcoinabc.org/D7721