Support callers with nounset enabled

[memotype]

Summary

• disable nounset inside the existing bj subshell
• add implementation-parameterized regression coverage for object, array, string, number, boolean, null, nested, and missing-key queries under bash -u
• verify that nounset remains enabled in the caller after bj returns
• regenerate all compact artifacts

Rationale

bj inherits shell options from its caller and intentionally uses omitted helper arguments as compact mode flags. Under nounset, those optional positional-parameter expansions abort otherwise valid queries. Disabling nounset at the start of the existing bj subshell contains the option change within each invocation, preserves caller state, and avoids expanding the parser control flow. It adds seven bytes to the canonical compact form without increasing the wrapped line counts.

Testing

• make verify
• make -B all
• git diff --exit-code

Closes #22