Fix enum selector

[goccy]

As a result of processing all enum values as opaque<int>, it was found that type errors occur when trying to create a message within a CEL expression using those values.

This behavior was unintended, so we will revert to processing them as int as before and convert them to opaque<int> only when necessary.

[github-actions[bot]]

Code Metrics Report

	main (dfe01be)	#202 (707a0d2)	+/-
Coverage	65.2%	65.1%	-0.1%
Code to Test Ratio	1:0.3	1:0.3	-0.0
Test Execution Time	7m16s	6m56s	-20s

Details

``` diff | | main (dfe01be) | #202 (707a0d2) | +/- | |---------------------|----------------|----------------|-------| - | Coverage | 65.2% | 65.1% | -0.1% | | Files | 69 | 69 | 0 | | Lines | 11439 | 11448 | +9 | | Covered | 7453 | 7453 | 0 | - | Code to Test Ratio | 1:0.3 | 1:0.3 | -0.0 | | Code | 36453 | 36474 | +21 | | Test | 12564 | 12564 | 0 | + | Test Execution Time | 7m16s | 6m56s | -20s | ```

Code coverage of files in pull request scope (80.9% → 80.5%)

Files	Coverage	+/-
grpc/federation/cel/enum.go	50.7%	-4.1%
resolver/error.go	63.6%	0.0%
resolver/resolver.go	82.0%	-0.2%

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Reported by octocov

[github-actions[bot]]

Code Metrics Report

	main (dfe01be)	#202 (bb340ea)	+/-
Coverage	65.2%	65.1%	-0.0%
Code to Test Ratio	1:0.3	1:0.3	-0.0
Test Execution Time	7m16s	7m3s	-13s

Details

``` diff | | main (dfe01be) | #202 (bb340ea) | +/- | |---------------------|----------------|----------------|-------| - | Coverage | 65.2% | 65.1% | -0.0% | | Files | 69 | 69 | 0 | | Lines | 11439 | 11448 | +9 | + | Covered | 7453 | 7457 | +4 | - | Code to Test Ratio | 1:0.3 | 1:0.3 | -0.0 | | Code | 36453 | 36474 | +21 | + | Test | 12564 | 12567 | +3 | + | Test Execution Time | 7m16s | 7m3s | -13s | ```

Code coverage of files in pull request scope (80.9% → 80.7%)

Files	Coverage	+/-
grpc/federation/cel/enum.go	50.7%	-4.1%
resolver/error.go	63.6%	0.0%
resolver/resolver.go	82.2%	+0.0%

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Reported by octocov