[wanda] Wire context owner override through tar writing

[andrew-anyscale]

Add an owner field to tarStream that, when set, overrides the uid/gid on all file entries written to the tar. Pass the owner through tarFile.writeTo so each file header gets the override applied.

Topic: add-context-owner-tar
Relative: add-context-owner

Co-Authored-By: Claude Opus 4.6 (1M context) noreply@anthropic.com
Signed-off-by: andrew andrew@anyscale.com

[andrew-anyscale]

Reviews in this chain:
└#479 [wanda] Add contextOwner type and parser
　└#480 [wanda] Wire context owner override through tar writing
　　└#481 [wanda] Add context_owner spec option and include in cache digest

[andrew-anyscale]

#	head	base	diff	date	summary
0	fac3b483	3a039ba0	diff	Apr 2 13:44 PM	4 files changed, 51 insertions(+), 5 deletions(-)
1	91254ad6	36e12bbe	diff	Apr 2 13:55 PM	4 files changed, 30 insertions(+), 9 deletions(-)
2	08d056c8	433015c0	diff	Apr 2 19:35 PM	0 files changed

[gemini-code-assist]

Code Review

This pull request introduces the ability to override UID and GID for all entries in a tar stream by adding an owner field to the tarStream struct and propagating it to the tarFile.writeTo method. While the implementation correctly updates the tar headers, the reviewer pointed out that the owner field is currently missing from the digest() calculation. This omission could lead to cache collisions where different ownership settings result in the same digest. It is recommended to include the owner information in the digest and add a test case to verify that digest values change when ownership is modified.

[github-actions]

⚠️ PR Size Warning

This PR exceeds the size limits defined in .buildkite/raycilint.yaml.

Break this into smaller PRs, or apply the skip-prcheck label to bypass.