shell: add --sync-exclude flag to exclude paths from --sync

[itsme-ranger]

Fixes #4887

Changes

Adds a --sync-exclude flag to limactl shell --sync that passes --exclude to all rsync operations (host→guest initial sync, the dry-run stats pass, and the guest→host sync-back).

# Exclude node_modules and .git from the sync
limactl shell --sync . --sync-exclude=node_modules --sync-exclude=.git default

# Use rsync glob patterns
limactl shell --sync . --sync-exclude='*.o' --sync-exclude=dist myinstance

The flag uses rsync's standard --exclude syntax and can be specified multiple times. Using --sync-exclude without --sync returns an error.

Implementation

• Added --sync-exclude as a StringArray flag on the shell command
• Built excludeArgs as ["--exclude", val, ...] pairs
• Threaded into the copytool.Options.AdditionalArgs of the initial sync CopyTool (which is also reused for rsync-back and the "view changes" diff)
• Added excludeArgs parameter to getRsyncStats so the dry-run stats pass applies the same filters

Testing

• go build ./cmd/limactl/ passes
• go test ./cmd/limactl/... passes
• golangci-lint run ./cmd/limactl/... reports 0 issues

[unsuman]

Seems duplicate of #4917