chore: update package.json to include TS declarations in ESM exports

[UzEE]

Problem

After #1130, consumers using TypeScript with moduleResolution: node16/nodenext/bundler get
TS7016 ... implicitly has an 'any' type ... could not be resolved when respecting package.json "exports" when importing twilio.

Cause

Type declarations aren’t exported via package.json "exports", so TS refuses to load them when respecting exports (discussion here).

Fixes

Add a "types" condition to the "." export so TypeScript can resolve ./index.d.ts while Node keeps using the JS entry points. TS docs describe this mechanism and recommend putting "types" first in the condition list.

Runtime impact

None. Node ignores "types". make test passes locally.

Checklist

• I acknowledge that all my contributions will be made under the project's license
• I have made a material change to the repo (functionality, testing, spelling, grammar)
• I have read the Contribution Guidelines and my PR follows them
• I have titled the PR appropriately
• I have updated my branch with the main branch
• I have added tests that prove my fix is effective or that my feature works
• I have added the necessary documentation about the functionality in the appropriate .md file
• I have added inline documentation to the code I modified