Fixes for line number node insertion in short form blocks

[c42f]

Copy some peculiar behaviors of the reference parser for compatibility:

• Top level blocks like a;b;c don't have any line numbers
• Blocks like (a;b;c) omit the first line number node

As part of this, add a new flag TOPLEVEL_SEMICOLONS_FLAG to distinguish semicolon-delimited toplevel statements from newline-delimited.

[codecov[bot]]

Codecov Report

Merging #279 (dfd0dfb) into main (0dcca2a) will increase coverage by 0.00%. The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main     #279   +/-   ##
=======================================
  Coverage   96.68%   96.68%           
=======================================
  Files          14       14           
  Lines        4007     4011    +4     
=======================================
+ Hits         3874     3878    +4     
  Misses        133      133           

Impacted Files	Coverage Δ
src/expr.jl	100.00% <100.00%> (ø)
src/parse_stream.jl	96.37% <100.00%> (+0.01%)	:arrow_up:
src/parser.jl	98.25% <100.00%> (ø)