fix(interpreter): initialize assoc/indexed arrays for local -A/-a

[chaliy]

Summary

• local -A m followed by m["a"]="1" produced an indexed array instead of associative, because execute_local_builtin only inserted into call_stack.locals without creating the assoc_arrays entry
• Initialize the appropriate array type when local -A or -a is used without a compound assignment value
• Fix applies to both function-scope and global-scope paths
• Add spec tests assoc_local_declare_then_assign and assoc_local_keys_in_cmdsub

Test plan

• New spec tests pass
• All 1812 bash spec tests pass (100%)
• Full cargo test --all-features passes
• cargo fmt --check and cargo clippy clean

Closes #875

[Copilot]

Pull request overview

Fixes local -A/-a declarations so arrays are initialized with the correct type even when declared without a compound assignment, aligning subsequent element assignments and key expansions with bash behavior.

Changes:

• Initialize assoc_arrays / arrays entries when local -A name / local -a name is used without =(...) (both function-scope and global-scope paths).
• Add spec coverage for local -A declared first, then populated via element assignments (including keys expansion inside $(...)).

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
crates/bashkit/src/interpreter/mod.rs	Ensures local -A/-a creates the corresponding array container upfront so later name[key]=... writes use the correct array type.
crates/bashkit/tests/spec_cases/bash/assoc-arrays.test.sh	Adds spec cases validating local -A declare-then-assign and key expansion captured via command substitution.

Comments suppressed due to low confidence (1)

crates/bashkit/src/interpreter/mod.rs:4514

• The PR updates local handling for both associative (-A) and indexed (-a) arrays, but the added spec tests only cover the local -A name; name[...]=... path. Please add a regression test for local -a arr declared without a compound assignment (e.g., local -a arr; arr[0]=...; echo ${#arr[@]}) to ensure the new flags.array initialization paths stay covered.

                let key = &arg[bracket + 1..arg.len() - 1];
                let expanded_key = self.expand_variable_or_literal(key);
                let resolved_name = self.resolve_nameref(arr_name).to_string();
                if let Some(arr) = self.assoc_arrays.get_mut(&resolved_name) {
                    arr.remove(&expanded_key);

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[Copilot]

Issue #875’s repro involves associative array key expansion inside a process substitution nested within a command substitution (result="$(... < <(... ${!m[@]} ...))"). The new assoc_local_keys_in_cmdsub test covers command substitution but not the nested process substitution case; consider adding a spec test that matches the reported pattern to prevent regressions in that scenario.