[sonic-slave-trixie]: Upgrade Rust toolchain to 1.88.0

[netobani]

Why I did it

The trixie build slave currently installs Rust 1.86.0. Some Rust crates used by SONiC's tooling have started requiring newer toolchains — most recently gimli 0.33.0 (pulled in by cargo-tarpaulin >= 0.35.2) which needs Rust 1.88+.

To keep the slave aligned with what the ecosystem expects, bump the toolchain to 1.88.0.

How I did it

• sonic-slave-trixie/Dockerfile.j2: bump rustup --default-toolchain from 1.86.0 to 1.88.0.
• Drop the cargo-tarpaulin@0.35.1 version pin and the accompanying comment — the pin was a workaround for the Rust 1.86 limitation and is no longer needed.

How to verify it

• Rebuild the trixie slave image: make sonic-slave-trixie-build
• Inside the slave: rustc --version should report 1.88.0, and cargo tarpaulin --version should resolve to the latest release.
• Run any Rust-based package builds (e.g. sonic-nettools, watchdog images) and confirm they still build clean.

[mssonicbld]

/azp run Azure.sonic-buildimage

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[banidoru]

• Clean, minimal change — toolchain bump + unpin looks correct.
• --locked on cargo-tarpaulin install is good; mitigates most supply-chain risk.
• Minor: unpinning cargo-tarpaulin means future builds pick up whatever's latest — if a broken release lands, slave builds break. Acceptable risk given the pin was a workaround, but worth noting.
• No cross-build or other Dockerfile.j2 sections affected.
• Commit is properly signed-off.

[banidoru]

• The removal of the version pin for cargo-tarpaulin makes the build non-reproducible and susceptible to future breakages.
• The version should be pinned to a specific, known-good version to ensure build stability.

[banidoru]

• Rust 1.86.0 → 1.88.0 bump is clean; single-file change, no side effects on cross-build or other Dockerfile sections.
• Removing the version pin comment is correct — the workaround reason (gimli 0.33.0 needing 1.88+) no longer applies.
• --locked retained on cargo install — good.
• Agree with existing feedback: re-pinning cargo-tarpaulin to the current latest (e.g. 0.35.2) would be better for reproducibility, but not blocking.
• Commit is signed-off and properly scoped.

[netobani]

Automated review follow-up:

• Addressed: pinned cargo-tarpaulin to 0.35.2 in sonic-slave-trixie/Dockerfile.j2 for reproducible builds (46034d8).

[mssonicbld]

/azp run Azure.sonic-buildimage

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[banidoru]

• Rust toolchain bump 1.86.0 → 1.88.0 looks correct and aligns with ecosystem requirements (gimli 0.33.0 needs 1.88+).
• cargo-tarpaulin now pinned to 0.35.2 with --locked — reproducibility concern from prior review is addressed.
• Old workaround comments removed cleanly; new comment explains the pin rationale.
• No other files affected; change is minimal and focused.
• LGTM.

[banidoru]

• The dependency is now pinned to version , ensuring reproducible builds.
• This change directly addresses all previous review feedback.
• No new issues were found in the diff.

[banidoru]

• Rust 1.86.0 → 1.88.0 upgrade is straightforward and correctly scoped to trixie slave only
• cargo-tarpaulin now pinned to 0.35.2 with --locked — addresses prior reproducibility concern
• Comment explaining the pin rationale is clear and helpful
• No other files affected; change is minimal and safe
• Prior review threads resolved appropriately

[banidoru]

All reviewers approved. LGTM.