build: reduce Rust dev debuginfo

[bolinfest]

What changed

This PR makes the default Cargo dev profile use line-tables-only debug info:

[profile.dev]
debug = 1

That keeps useful backtraces while avoiding the cost of full variable debug
info in normal local dev builds.

This also makes the Bazel CI setting explicit with -Cdebuginfo=0 for target
and exec-configuration Rust actions. Bazel/rules_rust does not read Cargo
profiles for this setting, and the current fastbuild action already emitted
--codegen=debuginfo=0; the Bazel part of this PR makes that choice direct in
our build configuration.

Why

The slow codex-core rebuilds are dominated by debug-info codegen, not parsing
or type checking. On a warm-dependency package rebuild, the baseline
codex-core compile was about 39.5s wall / 38.9s rustc total, with
codegen_crate around 14.0s and LLVM_passes around 13.4s. Setting codex-core
to line-tables-only debug info brought that to about 27.2s wall / 26.7s rustc
total, with codegen_crate around 3.1s and LLVM_passes around 2.8s.

debug = 0 was only about another 0.7s faster than debug = 1 in the
codex-core measurement, so debug = 1 is the better default dev tradeoff: it
captures nearly all of the compile-time win while preserving basic
debuggability.

I also sampled other first-party crates instead of keeping a codex-core-only
package override. codex-app-server showed the same pattern: rustc total
dropped from 15.85s to 10.48s, while codegen_crate plus LLVM_passes dropped
from about 13.47s to 3.23s. codex-app-server-protocol had a smaller but still
real improvement, 16.05s to 14.58s total, and smaller crates showed modest
wins. That points to a workspace dev-profile policy rather than a
hand-maintained list of large crates.

Relationship to #18612

#18612 added the dev-small
profile. That remains useful when someone wants a working local build quickly
and is willing to opt in with cargo build --profile dev-small.

This PR is deliberately less aggressive: it changes the common default dev
profile while preserving line tables/backtraces. dev-small remains the
explicit "build quickly, no debuggability concern" path.

Other investigation

I looked for another structural win comparable to
#16631 and
#16630, but did not find one.
The attempted TOML monomorphization changes were noisy or worse in
measurement, and the async task changes reduced some instantiations but only
translated to roughly a one-second improvement while being much more
disruptive. The debug-info setting was the one repeatable, material win that
survived measurement.

Verification

• just bazel-lock-update
• just bazel-lock-check
• cargo check -p codex-core --lib
• cargo test -p codex-core --lib
• Bazel aquery --config=ci-linux confirmed --codegen=debuginfo=0 and
  -Cdebuginfo=0 for //codex-rs/core:core

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• core: make test-log a dev dependency #18846
• -> build: reduce Rust dev debuginfo #18844