test(tlv): add unit tests and refactor tlv.go

[watal]

Description

• Fixed SRPolicyCandidatePathIdentifier to comply with RFC 9862/9256 (correct Originator IPv4 handling)
• Added missing TLV fields and MarshalLogObject implementations
• Improved padding and slice handling
• Enhanced JSON marshaling of (ts Psts) MarshalJSON()
• Replaced magic numbers with constants
• Consolidated common TLV decoding into decodeTLVLength
• Added error checks

Type of change

• New features (added TLV tests)
• Refactoring (improved TLV Serialize/Decode, helper functions)

Motivation and Context

To increase test coverage and improve readability and maintainability of TLV handling code.

How is This Tested?

• Verified TLV Serialize/Decode/MarshalLogObject using go test ./...
• Scenario tests in the test/ directory

Other Information

No additional information.

[Copilot]

Pull request overview

This PR expands and refactors PCEP TLV handling by introducing shared TLV parsing helpers, updating multiple TLV Encode/Decode implementations to use them, and adding extensive table-driven unit tests across TLV types.

Changes:

• Added decodeTLVLength, paddedLength, and isIPv4Bytes helpers and corresponding unit tests.
• Refactored multiple TLV DecodeFromBytes / Serialize / Len / MarshalLogObject implementations to use shared offsets/constants and stricter length validation.
• Greatly expanded TLV unit tests (decode/serialize/len/logging + DecodeTLV/DecodeTLVs cases) and added a capability test case for skipping LSPDBVersion.

Reviewed changes

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

Show a summary per file

File	Description
pkg/packet/pcep/tlv.go	Refactors TLV parsing/serialization, adds offsets/alignment constants, updates TLV map, and modifies DecodeTLVs logic.
pkg/packet/pcep/tlv_common.go	Introduces shared TLV helper utilities (length validation, padding, IPv4-bytes detection).
pkg/packet/pcep/tlv_common_test.go	Adds unit tests for the new TLV helper utilities.
pkg/packet/pcep/tlv_test.go	Reworks TLV tests into table-driven helpers and adds broad coverage across TLV types and TLV decoding.
pkg/packet/pcep/capability_test.go	Adds a test case asserting LSPDBVersion is skipped by PolaCapability.

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[Copilot]

Pull request overview

Copilot reviewed 5 out of 5 changed files in this pull request and generated 4 comments.

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[Copilot]

Pull request overview

Copilot reviewed 5 out of 5 changed files in this pull request and generated 3 comments.

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[Copilot]

Pull request overview

Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.

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[Copilot]

Pull request overview

Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.

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[Copilot]

Pull request overview

Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.

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[Copilot]

Pull request overview

Copilot reviewed 5 out of 5 changed files in this pull request and generated no new comments.

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[tatfujiwara]

minor comment