feat(tio-tool): Change RPC getopts style from FloatingFrees to StopAtFirstFree

[events555]

Motivation

getopts in its default FloatingFrees mod treats negative RPC arguments (e.g., -1) as flags when users invoke:

tio-tool rpc <rpc-name> -1

Based on our help text, users place [rpc-arg] immediately after <rpc-name> and thus the parsing style should be changed to StopAtFirstFree. This no longer requires marking -- to stop searching for flags (shown below).

tio-tool rpc <rpc-name> -- -1
tio-tool rpc -- <rpc-name> -1

Changes

• 71a3296 Switch tio-tool's rpc() to getopts::ParsingStyle::StopAtFirstFree so everything after <rpc-name> is treated as free (fixes negative args without requiring --).
• 070ebed Use util::default_proxy_url() as the actual fallback for -r
• c7f5966 Correct 64-bit request serialization (was previously using 32 bit types)
• 9fcf676 Change help text to --rep-type (not --ret-type)

How to Test

Verify tio-tool works on negative arguments

• tio-tool rpc field.cutoff -1

Also verify manual type specification of a RPC reply with -T/--rep-type