compiler: flatten parenthesized inline suites

[floitsch]

Part 9 of 10 in the AST-driven Toit pretty-printer stack. Depends on #3193.

Summary

• render parenthesized multi-expression suites with canonical semicolon separation
• support return, break, and continue inside parenthesized inline suites
• keep ordinary multi-statement suites multiline

Verification

• public-command gold cases cover parenthesized named blocks with assignment and return
• the changes close the final semantic-verification failures found by the 269-file corpus probe

_{Stack created with GitHub Stacks CLI}