lint: W002 (unused parameter) never fires for a function defined inside unobserved: or a match arm

[Nitjsefnie]

Describe the bug

W002 (unused parameter) is never reported for a function defined inside an unobserved: block or a match arm. check_unused_params recurses only through IF/FUNC/FOR/PROGRAM, and lists both AST_MATCH (src/lint.c:1530) and AST_UNOBSERVED (src/lint.c:1532) in its break-only group, so a nested define is never visited and the emission at src/lint.c:1475 is never reached.

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 w002_ctrl(unusedparam) as:
    return 1
w002_ctrl of 9

Silent — inside unobserved::

unobserved:
    define w002_u(unusedparam) as:
        return 1
w002_u of 9

Silent — inside a match arm:

match 1:
    case 1:
        define w002_m(unusedparam) as:
            return 1
    case _:
        x is 0
w002_m of 9

Expected behavior

warning[W002]: unused parameter 'unusedparam' in function '...' in all three, as the control already produces.

Actual behavior

$ eigenscript --lint w002_control.eigs
w002_control.eigs:1: warning[W002]: unused parameter 'unusedparam' in function 'w002_ctrl'
$ eigenscript --lint w002_unobs.eigs
w002_unobs.eigs: no issues found
$ eigenscript --lint w002_match.eigs
w002_match.eigs: no issues found

Both silent programs run (exit 0) and call the nested function, so these are reachable definitions.

Environment

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