fix(logger): gate OTLP/syslog/tokio stack for wasm32 targets

[p0wline]

Problem

opentelemetry-otlp (with grpc-tonic) pulls tonic → tokio (with the net feature) → mio, which does not compile for wasm32-unknown-unknown. This caused cosmian_kms_client_wasm builds to fail whenever cosmian_logger was a dependency.

Fix

All OTLP, syslog, and file-appender stacks are now restricted to cfg(not(target_arch = "wasm32")):

• Cargo.toml: OTLP/syslog deps moved to [target.'cfg(not(target_arch = "wasm32"))'.dependencies]
• src/error.rs: OTLP error variants gated
• src/types.rs: TelemetryGuards, LoggingGuards (with SDK fields) gated; wasm32 gets a no-op LoggingGuards stub
• src/lib.rs: all OTLP/syslog/file-appender code gated; wasm32 gets a no-op tracing_init()

On wasm32, tracing_init() is a no-op stub — downstream code should install a wasm-compatible subscriber (e.g. tracing_wasm) if log output is needed.

Verification

cargo build -p cosmian_logger                                    # native ✓
cargo build -p cosmian_logger --target wasm32-unknown-unknown    # wasm32 ✓
cargo clippy -p cosmian_logger --all-targets -- -D warnings      # zero warnings ✓

Bumps version 0.8.0 → 0.8.1.

[Copilot]

Pull request overview

This PR fixes wasm32-unknown-unknown build failures caused by opentelemetry-otlp (grpc-tonic → tokio/net → mio) by gating OTLP/syslog/file-appender logging functionality to non-wasm32 targets and providing no-op stubs on wasm32.

Changes:

• Move OTLP/syslog-related dependencies under target.'cfg(not(target_arch = "wasm32"))'.dependencies to avoid pulling tokio/mio on wasm32.
• Gate OTLP-related types/APIs and logging initialization logic to non-wasm targets, and provide a wasm32 no-op tracing_init() plus a stub LoggingGuards.
• Bump workspace version 0.8.0 → 0.8.1 (and update Cargo.lock).

Reviewed changes

Copilot reviewed 5 out of 6 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
crate/logger/src/types.rs	Adds cfg-gating for OTLP guard types and introduces a wasm32 LoggingGuards no-op stub.
crate/logger/src/lib.rs	Gates OTLP/syslog/file-appender initialization to non-wasm and adds a wasm32 no-op tracing_init().
crate/logger/src/error.rs	Gates OTLP-specific error variants to non-wasm targets.
crate/logger/Cargo.toml	Moves OTLP/syslog deps to non-wasm target deps; adjusts dependency placement.
Cargo.toml	Bumps workspace version to 0.8.1.
Cargo.lock	Updates locked crate versions to 0.8.1.

Comments suppressed due to low confidence (1)

crate/logger/Cargo.toml:44

• The tracing_example no longer has required-features, so it will be considered by --all-targets builds/lints for wasm32 even though it uses #[tokio::main] and sets TracingConfig::log_to_syslog (which is absent on wasm32 with the current cfg). This can reintroduce wasm32 build failures in CI when someone runs cargo clippy --all-targets --target wasm32-unknown-unknown. Gate the example behind a feature again (and define the feature) to keep default/wasm builds working.

[[example]]
name = "tracing_example"

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