fix: avoid throwing if caches is undeclared

[unkhz]

Problem
Using getAccessToken with a runtime that does not support the global caches property throws a reference error in any runtime that does not support the CacheStorage api. This happens during the support check for the default cache, which refers to the caches directly without having verified the support yet.

Solution
Use globalThis.caches to verify the reference.

[koistya]

@unkhz thanks, Juhani. Do you think we can use self.caches (for which Cloudflare provides type definitions) instead of globalThis.caches?

[unkhz]

I chose globalThis because it should be widely supported. Node 12.0.0+ and Deno 1.0+ supported (along with Bun 0.5.7, which I tested). It's also polyfilled in core-js for more ancient runtimes: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/globalThis#browser_compatibility.

Did a quick check and self seems to work nicely for Deno, Bun and Chrome, but throws reference error with Node.

[koistya]

Good catch! Just published these updates under v1.0.3.