fix: split YAML documents with the Kubernetes YAML reader

[MPV]

What

Split YAML documents with apimachinery's YAMLReader (via a new streaming yamlparser.ProcessReader) instead of bytes.Split on the literal "\n---\n".

Before → After

A two-document manifest whose separator has trailing whitespace — --- followed by spaces, common in hand-edited and templated YAML:

$ kir pods.yaml

# before
img-a:1                    # second document silently dropped: "\n---   \n" != "\n---\n"

# after
img-a:1
img-b:2

Verified against master. CRLF (\r\n) line endings are the other real case — bytes.Split misses that separator too and drops everything after the first document. (Leading --- and a missing final newline are not affected; they're kept in the unit test only as general correctness checks.)

Why

bytes.Split on the literal separator is fragile: any variation glues documents together so every one after the first is lost. Both the file and stdin paths now stream through one ProcessReader, so their splitting behaves identically and matches how Kubernetes itself parses manifests.

Note on error text

Returning ProcessData's error directly also drops the redundant error processing document: wrapper, so a genuine parse failure now reads error: <cause> instead of error: error processing document: <cause>.

Release

Based on master. fix: → patch.

🤖 Generated with Claude Code

https://claude.ai/code/session_01Pc6NAURAqjU4LYJx93tgSC