Support blocks with implicit parameters (_1, it) and backtick commands

[apiology]

Three block and literal forms have no type at --level strong, so calls on
them are unresolved and enclosing methods lose their return type.

# @return [Array<String>]
def numbered
  'a,b'.split(',').map { _1.upcase }   # Unresolved call to _1
end

# @return [Array<String>]
def implicit_it
  'a,b'.split(',').map { it.upcase }   # Unresolved call to it
end

# @return [String]
def backticks
  `hostname`.strip                     # Unresolved call to strip
end

All are clean in explicit form. A wrong tag also passes silently on the
implicit block form: @return [Array<Integer>] on
'a,b'.split(',').map { it } reports nothing.

_1 produces a numblock node, so the call was chained as though no block
were passed. it arrives as an ordinary block missing only its parameter —
hence the silent pass. Backticks produce an xstr node, absent from the
literal type table. Neither block form records parameters as an args node
does, so both are synthesized; a local named it still wins, matching Ruby.

This PR was written by Claude Code on behalf of @apiology.