Add builder for Backoff

[kth496]

Motivation:

• #5483

Modifications:

• Add Builder class for various backoff implementations.

Result:

• Closes #5483
• Will be able to use the builder class to create instances of BackOff.

[kth496]

@ikhoon Thank you for your review. I will fix it within a week.

[trustin]

@kth496 Looking forward to seeing more commits in this PR :heart_decoration:

[trustin]

@kth496 Any updates?

[github-actions[bot]]

🔍 Build Scan® (commit: 75753598cfefe8d8c19f66d4187b32d6a2a7c7db)

Job name	Status	Build Scan®
build-ubicloud-standard-8-jdk-8	✅	https://ge.armeria.dev/s/dm3hkglifq27s
build-ubicloud-standard-8-jdk-21-snapshot-blockhound	✅	https://ge.armeria.dev/s/7tt6wjdgqac36
build-ubicloud-standard-8-jdk-17-min-java-17-coverage	✅	https://ge.armeria.dev/s/guvjad7vttj56
build-ubicloud-standard-8-jdk-17-min-java-11	✅	https://ge.armeria.dev/s/kqe4dqojq3it4
build-ubicloud-standard-8-jdk-17-leak	✅	https://ge.armeria.dev/s/7x7254bs2utd6
build-ubicloud-standard-8-jdk-11	❌ (failure)	https://ge.armeria.dev/s/zmddfogavz4l2
build-macos-12-jdk-21	✅	https://ge.armeria.dev/s/c4t4v7dcuug6k

[kth496]

@ikhoon @trustin Thanks for patience. I have improved the code based on your feedback:

• Moved the nested classes into top-level classes
• Moved the builder methods to the BackOff interface

Question: Is there a good way to make the jitter value configurable in the builder? Since jitter can be commonly set across multiple BackOff implementations, I'm considering whether to define a separate higher-level builder.

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 83.87097% with 5 lines in your changes missing coverage. Please review.

Project coverage is 74.68%. Comparing base (9a29b39) to head (7575359). Report is 35 commits behind head on main.

Files with missing lines	Patch %	Lines
...corp/armeria/client/retry/FixedBackoffBuilder.java	0.00%	4 Missing :warning:
...ava/com/linecorp/armeria/client/retry/Backoff.java	75.00%	1 Missing :warning:

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #5488      +/-   ##
============================================
+ Coverage     74.66%   74.68%   +0.01%     
- Complexity    21681    21725      +44     
============================================
  Files          1896     1901       +5     
  Lines         80320    80414      +94     
  Branches      10548    10553       +5     
============================================
+ Hits          59974    60059      +85     
- Misses        15318    15324       +6     
- Partials       5028     5031       +3     

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