ESM-compatible builds are not being generated

[mcmire]

Only CommonJS-compatible builds are being generated, which means this library will not work in an ESM-only setting.

We should be using ts-bridge to build this package rather than straight tsc.

Acceptance Criteria

• Running yarn build should produce CommonJS- and ESM-compatible variants (i.e., .cjs, .mjs, .d.cts, and .d.mts variants should be present in dist/) via ts-bridge`
• The build:clean package script should not exist
• Arbitrary subimports should not be possible (there should only be two exports, . and ./package.json, and they should point to both CommonJS and ESM variants)