lint: W003 (unreachable code) never fires for a function defined inside unobserved: or a match arm

[Nitjsefnie]

Describe the bug

W003 (unreachable code after return) is never reported for a function defined inside an unobserved: block or a match arm. check_func_unreachable only scans bodies of AST_FUNC nodes its walker reaches, and both AST_MATCH (src/lint.c:1364) and AST_UNOBSERVED (src/lint.c:1366) sit in its break-only group — so the body is never handed to check_unreachable (src/lint.c:1308) and the emission at src/lint.c:399 never fires.

Surfaced while doing #779, which made these switches enumerable; it neither caused nor fixed this. Line numbers resolved against main @ 23edbc25.

To reproduce

Control — reported correctly:

define w003_ctrl() as:
    return 1
    dead_stmt is 2
w003_ctrl of null

Silent — inside unobserved::

unobserved:
    define w003_u() as:
        return 1
        dead_stmt is 2
w003_u of null

Silent — inside a match arm:

match 1:
    case 1:
        define w003_m() as:
            return 1
            dead_stmt is 2
    case _:
        x is 0
w003_m of null

Expected behavior

warning[W003]: unreachable code after return in all three.

Actual behavior

$ eigenscript --lint w003_control.eigs
w003_control.eigs:3: warning[W003]: unreachable code after return
$ eigenscript --lint w003_unobs.eigs
w003_unobs.eigs: no issues found
$ eigenscript --lint w003_match.eigs
w003_match.eigs: no issues found

Environment

• OS: Debian 13 (x86_64)
• GCC version: 14
• EigenScript version: 0.34.0 (main @ 23edbc25)