Add public rust_binary targets for rust_kvs examples

[Subramanian-K812]

Summary

Adds four rust_binary targets to src/rust/rust_kvs/BUILD — one for each
existing example source file in src/rust/rust_kvs/examples/.

Why

The rust_kvs crate already ships example source files (basic.rs,
custom_types.rs, defaults.rs, snapshots.rs) but they had no Bazel build
targets. Without targets, external packages cannot reference these examples for
bundling or showcase use, forcing them to maintain their own copies of the demo
code.

[github-actions]

License Check Results

🚀 The license check job ran with the Bazel command:

bazel run --lockfile_mode=error //:license-check

Status: ⚠️ Needs Review

Click to expand output

[License Check Output]
Extracting Bazel installation...
Starting local Bazel server (8.6.0) and connecting to it...
INFO: Invocation ID: a72f1589-fba5-4a14-b029-c557ee2d2ea1
Computing main repo mapping: 
Computing main repo mapping: 
Computing main repo mapping: 
Computing main repo mapping: 
Loading: 
Loading: 3 packages loaded
Loading: 3 packages loaded
    currently loading: 
Loading: 3 packages loaded
    currently loading: 
Loading: 3 packages loaded
    currently loading: 
Loading: 3 packages loaded
    currently loading: 
Analyzing: target //:license-check (4 packages loaded, 0 targets configured)
Analyzing: target //:license-check (4 packages loaded, 0 targets configured)

Analyzing: target //:license-check (27 packages loaded, 10 targets configured)

Analyzing: target //:license-check (85 packages loaded, 10 targets configured)

Analyzing: target //:license-check (137 packages loaded, 2680 targets configured)

Analyzing: target //:license-check (146 packages loaded, 6462 targets configured)

Analyzing: target //:license-check (153 packages loaded, 7962 targets configured)

Analyzing: target //:license-check (158 packages loaded, 8011 targets configured)

Analyzing: target //:license-check (158 packages loaded, 8011 targets configured)

Analyzing: target //:license-check (158 packages loaded, 8011 targets configured)

Analyzing: target //:license-check (158 packages loaded, 8011 targets configured)

Analyzing: target //:license-check (162 packages loaded, 10023 targets configured)

INFO: Analyzed target //:license-check (163 packages loaded, 10149 targets configured).
[1 / 15] [Prepa] Creating source manifest for //:license.check.license_check ... (3 actions, 0 running)
[13 / 17] JavaToolchainCompileClasses external/rules_java+/toolchains/platformclasspath_classes; 0s disk-cache, processwrapper-sandbox ... (2 actions running)
INFO: From Generating Dash formatted dependency file ...:
INFO: Successfully converted 66 packages from Cargo.lock to bazel-out/k8-fastbuild/bin/formatted.txt
[15 / 17] JavaToolchainCompileBootClasspath external/rules_java+/toolchains/platformclasspath.jar; 0s disk-cache, processwrapper-sandbox
INFO: Found 1 target...
Target //:license.check.license_check up-to-date:
  bazel-bin/license.check.license_check
  bazel-bin/license.check.license_check.jar
INFO: Elapsed time: 25.312s, Critical Path: 2.41s
INFO: 17 processes: 12 internal, 4 processwrapper-sandbox, 1 worker.
INFO: Build completed successfully, 17 total actions
INFO: Running command line: bazel-bin/license.check.license_check ./formatted.txt <args omitted>
usage: org.eclipse.dash.licenses.cli.Main [-batch <int>] [-cd <url>]
       [-confidence <int>] [-ef <url>] [-excludeSources <sources>] [-help] [-lic
       <url>] [-project <shortname>] [-repo <url>] [-review] [-summary <file>]
       [-timeout <seconds>] [-token <token>]