fix(graph): make graph format explicit

[schmidma]

Description

GitHub shows this PR against main, but the intended review base is #161.

Make graph backend selection explicit by changing Graph::new to require a KeyExprFormat, and align ZContextBuilder so the context-owned graph uses the same format selected via .keyexpr_format(...).

This fixes an inconsistency where nodes, publishers, subscribers, and services respected the context format, but the internal graph always used the default RmwZenoh parser and pattern.

It also restores correct behavior for graph-backed helpers under Ros2Dds, including publisher and subscriber matching via the context-owned graph.

Checklist

• Ran ./scripts/check-local.sh successfully
• Added or updated tests and documentation when applicable

[codecov]

Codecov Report

❌ Patch coverage is 76.15572% with 98 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
crates/ros-z/src/graph.rs	70.73%	36 Missing ⚠️
...rates/ros-z/src/dynamic/type_description_client.rs	76.59%	22 Missing ⚠️
crates/ros-z/src/pubsub.rs	54.16%	11 Missing ⚠️
crates/ros-z-protocol/src/entity.rs	72.72%	9 Missing ⚠️
crates/ros-z-protocol/src/format/rmw_zenoh.rs	92.68%	6 Missing ⚠️
crates/ros-z/src/entity.rs	54.54%	5 Missing ⚠️
crates/ros-z/src/dynamic/error.rs	0.00%	4 Missing ⚠️
...ates/ros-z/src/dynamic/type_description_service.rs	0.00%	3 Missing ⚠️
crates/ros-z/src/service.rs	80.00%	2 Missing ⚠️

Files with missing lines	Coverage Δ
crates/ros-z/src/action/client.rs	67.52% <ø> (ø)
crates/ros-z/src/action/server.rs	74.38% <ø> (ø)
crates/ros-z/src/config.rs	81.62% <ø> (ø)
crates/ros-z/src/context.rs	50.59% <100.00%> (ø)
crates/ros-z/src/encoding.rs	95.37% <ø> (ø)
crates/ros-z/src/event.rs	87.57% <100.00%> (+0.25%)	⬆️
crates/ros-z/src/node.rs	50.66% <100.00%> (ø)
crates/ros-z/src/parameter/service.rs	78.74% <100.00%> (ø)
crates/ros-z/src/shm.rs	62.74% <ø> (ø)
crates/ros-z/src/service.rs	73.66% <80.00%> (-0.57%)	⬇️
... and 8 more

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