Windows: absolute bind-mount sources (C:\path:/container) are misparsed as named volumes

[jssblck]

Summary

On Windows, an absolute host bind mount like volume=C:\data:/var/lib/data does not work. eph treats it as a named volume rather than a host bind, and the drive-letter colon breaks the spec split.

Split off from #44 (which fixed the separate relative-bind \?\ issue). These are distinct bugs; #44's fix is complete without this.

Diagnosis

resolve_volume_spec (src/service.rs) decides host-path vs named-volume by whether the spec starts with / or .:

if spec.starts_with('/') || spec.starts_with('.') {
    // host-path bind mount
} else {
    // named volume, namespaced
}

An absolute Windows path starts with a drive letter (C), not / or ., so C:\data:/var/lib/data falls into the named-volume branch. On top of that, the spec is split with splitn(2, ':'), which lands on the drive-letter colon:

• "C:\data:/var/lib/data" splits into ["C", "\data:/var/lib/data"]

So the "volume name" becomes C and the "container path" becomes \data:/var/lib/data. The result is a bogus namespaced named volume, not the intended host bind. A verbatim \?\C:\... absolute source has the same problem (starts with \, drive colon inside).

Proper fix

This needs a real volume-spec parser rather than splitn(2, ':'), one that understands Windows drive letters (X:\...), the \?\ and UNC forms, and the [host]:[container][:mode] shape with a Windows-aware split (Docker's own client special-cases a single leading drive letter before splitting on :). A drive-letter or backslash prefix should route to the host-path branch, and the split must not treat the drive colon as the host/container separator.

Repro

[svc]
image=alpine
volume=C:\Users\me\data:/data

eph up

Expected: C:\Users\me\data bind-mounted at /data. Actual: a namespaced named volume derived from C is created instead.

Scope note

Relative binds (./seed:/x) and Unix-style absolute binds (/host/path:/x) are unaffected and work today. This is specifically about Windows drive-letter absolute sources.