fix(core): break reference chain to instance object

[breeeew]

Reference caused in getContextFactory, and it stored in handlerMetadataStorage in Map, that never be purged

PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/nestjs/nest/blob/master/CONTRIBUTING.md
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Other... Please describe:

What is the current behavior?

issue

Issue Number: 13365

What is the new behavior?

same, but without leak

Does this PR introduce a breaking change?

• Yes
• No

Other information

[breeeew]

Sorry, but I can't figure out how to write tests for this

[coveralls]

Pull Request Test Coverage Report for Build 313c391e-2e75-4829-9f2c-92b11880aea0

Details

• 2 of 3 (66.67%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 92.146%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
packages/core/helpers/context-utils.ts	2	3	66.67%

Totals
Change from base Build 6bb059e7-7c5e-42b3-ae34-83ddafc5213b:	0.0%
Covered Lines:	6734
Relevant Lines:	7308

---

💛 - Coveralls

[kamilmysliwiec]

LGTM