fix: parse dvm's key=value format in .dvmrc

[somaz94]

The README documents that deno-version-file can read dvm's .dvmrc, but the parser only accepts a bare version string. dvm writes the file as key=value (configrc.rs serializes with format!("{}={}", k, v)), so deno_version=1.43.1 falls through to the bare-version branch and fails with The passed version range is not valid.

.dvmrc is a general key/value store rather than a single line, and dvm also records registry_binary / registry_version, so the version is not necessarily on the first line. The new pattern scans every line for the deno_version key. It runs only after the existing .tool-versions match, and the two patterns are disjoint, so bare-version and .tool-versions files behave exactly as before.

Also tolerates spaces around = (dvm's own reader trims both sides) and a v prefix, consistent with the existing .tool-versions handling.

Validation:

• deno lint, deno fmt --check, deno check src/main.ts all pass locally
• deno run -A scripts/build.ts rebuilt dist/, and a second build is byte-identical, so build-diff stays clean
• New test-version-file-dvm job writes a dvm-style .dvmrc with deno_version on the second line, so it covers the multi-key case rather than just a prefix strip
• Exercised the parser locally over 13 cases: dvm single-key / multi-key in both orders / spaces around = / v prefix / CRLF, plus regressions for bare version, bare range (~1.32), .tool-versions, and a my_deno_versionx= string that must not match

related: #121

[somaz94]

Heads up on the red CI, both failures are pre-existing on main and not from this change.

lint fails at deno check src/main.ts because canary now declares ImportMeta.dirname/filename as string, which conflicts with the optional re-declaration at src/main.ts:13-14. I reproduced the same 4 errors on an unmodified main checkout with the same canary build.

test (ubuntu-latest, 4e8b2f46...) fails with a 404 from dl.deno.land for that pinned canary hash, so the artifact looks expired.

The jobs this PR affects are green: build-diff, test-version-file (.dvmrc and .tool-versions), and the new test-version-file-dvm.

Happy to fix either one in a separate PR if that helps.