add multi-document yaml read util function

[vkumbhar94]

Currently pkgxdev is failing to autodetect skaffold when skaffold.yaml is having multiple documents with following error:

╰─ z skaf                                                                                                            ─╯
-deno.land -deno^2 -nodejs.org
error: Uncaught (in promise) SyntaxError: Found more than 1 document in the stream: expected a single document
    throw new SyntaxError(
          ^
    at parse (https://jsr.io/@std/yaml/1.0.5/parse.ts:87:11)
    at Path.readYAML (https://raw.githubusercontent.com/pkgxdev/libpkgx/refs/tags/v0.20.1/src/utils/Path.ts:405:14)
    at eventLoopTick (ext:core/01_core.js:177:7)
    at async skaffold_yaml (file:///Users/vkumbhar94/.pkgx/pkgx.sh/dev/v1.5.0/share/pkgx/dev/src/sniff.ts:263:18)
    at async default (file:///Users/vkumbhar94/.pkgx/pkgx.sh/dev/v1.5.0/share/pkgx/dev/src/sniff.ts:61:11)
    at async default (file:///Users/vkumbhar94/.pkgx/pkgx.sh/dev/v1.5.0/share/pkgx/dev/src/dump.ts:6:17)
    at async file:///Users/vkumbhar94/.pkgx/pkgx.sh/dev/v1.5.0/share/pkgx/dev/app.ts:48:7
Caused by: "skaffold-modules/skaffold.yaml"