Reset keyToScope and lastScope in ScopeInfoBuilder.build() so a reused builder does not leak state

[gunjanjaswal]

Summary

ScopeInfoBuilder.build() returns the accumulated ScopeInfo and resets the builder so it can be reused. It clears #scopes, #ranges, and #knownScopes, but leaves #keyToScope and #lastScope populated, so state from a previous build leaks into the next one.

If you reuse a builder across two build() calls, a startRange({ scopeKey }) in the second build resolves originalScope from a key registered during the first build, linking the range to a scope that is not part of the current tree. Encoding that result then throws Unknown OriginalScope for definition!. A freshly constructed builder produces no such link. lastScope() has the same leak: it returns a scope from the prior build after a build() that opened none.

Fix

Clear #keyToScope and reset #lastScope in build(), alongside the existing resets.

Test

Added a case in builder.test.ts: register key: 0 and build once, then in a second build resolve scopeKey: 0 and assert the range's originalScope is undefined (and lastScope() is null). It fails before the change and passes after.