prefer bin as directory name to hold binaries

[zancas]

Local sanity check run after the name change:

getrawtransaction_sidechain.py:
Pass: True, Duration: 0 s

feature_nu6.py:
Pass: True, Duration: 1 s
......
indexer.py:
Pass: True, Duration: 3 s
..
fix_block_commitments.py:
Pass: True, Duration: 5 s
.........................
feature_backup_non_finalized_state.py:
Pass: True, Duration: 19 s
.......................................
addnode.py:
Pass: True, Duration: 39 s
TEST                                  | PASSED | DURATION

addnode.py                            | True   | 39 s
feature_backup_non_finalized_state.py | True   | 19 s
feature_nu6.py                        | True   | 1 s
fix_block_commitments.py              | True   | 5 s
getrawtransaction_sidechain.py        | True   | 0 s
indexer.py                            | True   | 3 s
ALL                                   | True   | 67 s (accumulated)
Runtime: 39 s

[nuttycom]

Please grep the codebase for all remaining instances of "src" and inspect them individually to ensure you catch everything.

[zancas]

I have not confirmed that CI runs, which is necessary to validate the numerous changes inside .github.