log: add OpenTelemetry + text log renderers

[achille-roussel]

Summary

• New stripes/log package — one renderer for both OpenTelemetry log batches (binary / protojson, MIME application/vnd.opentelemetry.logs) and line-oriented text log formats (logfmt, jsonlog, AWS ALB, NGINX, log4j/Kafka, Python logging, Go stdlib log, BSD/RFC 5424 syslog).
• Unified per-record layout: yyyy/mm/dd hh:mm:ss.mmm LEVEL metadata message header with attributes indented underneath, keys aligned on a │ separator. Timestamps normalise to local time; severity is a fixed 4-char coloured label (TRAC/DEBU cyan, INFO green, WARN yellow, ERRO red, FATA purple).
• HTTP access logs drop the level column (status code carries severity), surface every documented ALB field as attrs named per AWS docs, colour the HTTP method by class (GET blue, POST orange, PUT magenta, PATCH purple, DELETE pink), and dim the HTTP/x.y version suffix.
• Multi-line content folds into the preceding record's message: matching lines start a new record; non-matching and whitespace-prefixed lines append to it. Go panic dumps and exception traces render verbatim (no wrapper indent) so their own indentation shows through.
• CLI gains per-format --format aliases and derives compression from the filename when Content-Encoding is absent, so s3://…/foo.log.gz "just works."
• json/detectJSON tightened to require a parseable first JSON value, so log4j's bracketed timestamps no longer false-positive into the JSON renderer.

Test plan

• go build ./... clean
• go vet ./... clean
• gofmt -l . clean
• go test -count=1 ./... — all packages green, including the existing testdata/script/*.txtar detection-priority tests
• New testdata/script/detect_log.txtar covers content-based detection across every text log format
• testdata/log/ fixtures render correctly under their auto-detected format and under explicit --format= flags
• testdata/log/otlp.binpb (regenerable via go run ./testdata/log/gen) renders under both --format=logs and --schema=opentelemetry.proto.logs.v1.LogsData
• Manual smoke against a real s3://…elasticloadbalancing/…log.gz (auto-decompresses, auto-detects ALB)

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