feat: top level scalar value plan.

[Peefy]

1. Does this PR affect any open issues?(Y/N) and add issue references (e.g. "fix #123", "re #123".):

• N
• Y

feat: #545 top-level scalar value plan.

2. What is the scope of this PR (e.g. component or file name):

• kclvm/compiler/src/codegen/llvm/context.rs
• kclvm/compiler/src/codegen/llvm/node.rs

3. Provide a description of the PR(e.g. more details, effects, motivations or doc link):

• Affects user behaviors
• Contains syntax changes
• Contains variable changes
• Contains experimental features
• Performance regression: Consumes more CPU
• Performance regression: Consumes more Memory
• Other

4. Are there any breaking changes?(Y/N) and describe the breaking changes(e.g. more details, motivations or doc link):

• N
• Y

5. Are there test cases for these changes?(Y/N) select and add more details, references or doc links:

• Unit test
• Integration test
• Benchmark (add benchmark stats below)
• Manual test (add detailed scripts or steps below)
• Other

• test/grammar/scalar/config/**

6. Release note

Please refer to Release Notes Language Style Guide to write a quality release note.

None

[coveralls]

Pull Request Test Coverage Report for Build 5042375457

• 60 of 66 (90.91%) changed or added relevant lines in 3 files are covered.
• 31 unchanged lines in 1 file lost coverage.
• Overall coverage decreased (-20.0%) to 68.029%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
kclvm/compiler/src/codegen/llvm/context.rs	43	45	95.56%
kclvm/runtime/src/value/val_union.rs	13	17	76.47%

Files with Coverage Reduction	New Missed Lines	%
compiler_base/session/src/lib.rs	31	50.0%

Totals
Change from base Build 5020425996:	-20.0%
Covered Lines:	30824
Relevant Lines:	45310

---

💛 - Coveralls

[zong-zhe]

LGTM